Here's the problem: she seems to be completely unable to express her emotions verbally. I can count the times she has complimented me on one hand. We go to school together, but when school isn't in session we are long distance. Even when we've been separated for several weeks she can't say "I miss you."
Those are things I had to *learn* to do. Complimenting I learned back when I was 18 and I went as an exchange student to Western Canada. As for expressing my emotions verbally, I first learned to express them in the *written* form. My future husband and I had an almost exclusively long-distance relationship up until we got married, so we used mail and IM to communicate. This was truly a blessing in disguise, as it gave me time to practice "saying" emotional stuff to him without actually *talking*. HOWEVER! After months of e-dating, when we met for the second time in person (the first time being when we actually met each other), my then-boyfriend was actually floored by the HUGE difference in behaviour I exhibited. I had become EXTREMELY expressive in writing, but when we met again, I just COULDN'T act accordingly. I was horribly tense, horribly silent, horribly guarded. I didn't WANT to be like that, but I didn't KNOW how to bridge the gap between my online persona and my real life persona. It was like I was two people at once, with my bubbly online persona stuck inside my guarded real life one. Luckily, my husband made all the right moves and with a bit of time I was able to relax enough to allow my inside persona to get out and take over. Since then, I've actually become the more verbally expressive of the two, and he's an ENFJ, so that says a bit
But to be honest, if I hadn't had the luxury of learning to express my feelings in written form first, I'm not sure I would ever have learned to express them in verbal form. As others have said, expressing my feelings can come easily when someone is in distress, but not so at all in day-to-day life. Like for example, I never say "I love you" to my parents or sister. I write it down on birthday cards, but I don't say it.
I think one thing about INFJs is that we are Introverts, so we live our life mostly inside ourselves. Expressing verbally what we think inside is NOT at all a given!
Another thing is that with Fe as our Auxiliary, we are *extremely* sensitive to rejection. So on one hand we are not likely to challenge a status quo in a relationship if we feel the other person is OK with it as it is, but on the other hand we feel hurt if the other person challenges a status quo that seems fine to us! I suspect something of that order might be happening with your girlfriend: she might already be doing her best, and she feels hurt because you're basically telling her that it's still not enough.
I don't mean to imply that she is cold, obviously as an INFJ this isn't the case. I can tell that she cares through sweet little gestures. However, I'm a tremendously verbal person, and it hurts my feelings a little bit that she can't just say "I care about you."
Inversely, she might be hurt by the fact that her gestures aren't enough for you. She might not see what's so special about *saying* stuff, so she might be feeling like you're accusing her of not really loving you.
Is it a time issue? Do I just have to earn the trust and loyalty of the INFJ over a longer period of time?
Maybe, but not necessarily. I fell for my husband very quickly.
However, earning her trust and loyalty might be a part of it, yes. But it's not so much a matter of time as a matter of doing the "right" things. One such big right thing is showing appreciation when she does a loving gesture towards you. You showing her that you do notice her gestures would in effect tell her that you know and realise that she does love you. This would make her feel much more secure in her relationship with you, and she would be far more likely to go out on a limb and try to give you what you have said you want, no matter how awkward it would make her feel at first.
A couple things: she actually seems like she's gotten less outwardly affectionate since we started actually dating, like now that she's officially admitted that she cares she's vulnerable or something.
I TOTALLY recognise myself in that one!! When my e-relationship with my future husband turned from e-friendship to e-dating, I was scared out of my skin! That was because I was feeling so incredibly vulnerable, and I was SOOOOOO afraid he would end up walking all over my heart. One of the hardest things I've ever done in my life was send him an email telling him just how incredibly vulnerable I was feeling. Strangely enough, I thought this would *repulse* him, which is one reason I wrote the email, so he would dump me sooner rather than later. When he wrote back saying that on the contrary my email made him want to run to me, I could hardly believe it.
So yes, at least in my case, admitting to my romantic feelings made me feel vulnerable and like wanting to run away.
She is emotionally affectionate, just not verbally, I guess that's the real issue.
My suggestion would be to start emailing and IMing more. Typically, INFJs are far more expressive in written form than verbal form. But do make sure that you do NOT expect her to be as expressive verbally the next day when you meet in person again! For an Extravert like you, this may feel very unsettling, like you're dating two different girls, but, well, Introverts DO tend to feel like they are two different people in one wrap. And the trick if you love one of us is to understand and ACCEPT that.
I also have to wonder if inexperience could be part of it. We're pretty young and neither one of us has very much dating experience.
Absolutely. Both life and dating experience, or rather the lack thereof, would have a huge effect on her ability to express herself.
Also, I tend to be pretty heavily emotionally expressive. I'm the type of person that says "I miss you" a ton, I like to compliment my partner, and this seems to make her a bit uncomfortable, which makes me wonder if that's why a lot of people put INFJ/ENTP as a better match. Maybe I'm just too emotionally volatile for her.
Even now, I still don't know how to take a compliment, even from my husband. I've *learned*, consciously learned, to just smile and say "thank you", but it's more of a coping technique than anything else.
Moreover, it could be that she feels desperate if she thinks that you expect her to actually measure up to your level of verbal expression. When under stress, INFJs can get into an "all or nothing" mentality: either I climb the Everest tonight, or I don't even try practicing climbing at all. So she might feel like, since she just cannot emulate your level of verbal expression *right now*, she might as well not try at all. The best way to deal with that is to notice when she *does* express herself, but not in an over-the-top way: something like a big smile and a thanks and a hug or a kiss, to assure her that you noticed her verbal efforts and that you truly appreciate them, but that you don't actually expect her to always be at that level from now on. See what I mean?
In short: make her feel SAFE! Make her feel like she's truly honestly fine the way she is, first and foremost! Once she feels safe, she will *on her own* look for ways to give you what you want.
The opposite, making her feel like you are somehow dissatisfied with the way she is now, is garanteed to make her feel miserable and to ultimately lead to her slowly detaching herself from you.
for you, INTJMom), but still, my mom pretty much never said "I love you" either. Which I am pretty sure comes from her own parents (the more I learn about her family, the more I'm convinced it was seriously dysfunctional). So I in turn never felt like saying it. What changed that was the opportunity to practice "saying" those things in written form*, and the fact that I don't actually use my mother tongue with my husband, so it didn't feel as weird when I started saying it out loud. Now I can say it in English to my husband, and both in English and in French to my son. But I still don't say it to my mom and sis, it would freak them (and me!) out I think if I did 
I think I would have gone all stony or something 
