Man, if only I could have been paid for how much I related to Skyward's original post.
I've felt the EXACT same way for many years. I think it really started for me at the very beginning of high school. Don't get me wrong, grammar school was definitely not a great experience, but people made sense to me back then. Socially, you could be more straight up with people, and for better or for worse, people were more honest. That meant more fighting and insults, but at least the kids were being honest about how they truly felt. Also, it was easier to make close friends at that time, for me.
Then, in high school, people began acting very different. Honesty just went out the window. Mean-ness was still there, naturally, but turned more and more into a strange version of passive aggression. Mainly, the already very prevalent pressure to "fit in" and "be normal" just seemed to go through the roof. If you were not "normal", there was always someone there to remind you, usually passively by excluding you quietly. But, you knew what was going on, even if the others weren't aware of it themselves. People just knew I wasn't like them. They liked me, but deep down, whether they were conscious of it or not, they did not go out of their way to include me in most of their social events like they did for the others who were MORE LIKE THEY WERE. In all honesty, it took me a long time to understand what it was about some people that made them so popular. Maybe having a certain look, or a certain personality factor played big points. But I was good looking, and a very nice kid (sorry if I'm bragging here), so it was confusing for me that I felt like such an alien. But, that was the way it was, and it continued with me for the most part through college, although my work ethic brought me success and (finally) a niche where I truly felt comfortable.
I had the same problems the original poster had; even other introverts puzzled me a lot of the time. Introverted thinkers seemed to have an easier time in school, and life than I did (unless they were so introverted they could hardly function socially). Introverted sensors could relate to me, but had it easier because there were more people like them around. Introverts who were more like I was either didn't exist where I was from or were so good at hiding their true selves that I could not identify them. Not to mention that I usually went to big schools where looking for introverts was like looking for needles in a haystack anyhow.
I have had a few moments in my life where I genuinely did fit in and was the center of what was happening. I cherish those moments, and I always will, because it took a lot of work to get to and maintain those moments. Most of my friends (extroverts), with all due respect, were great people, but could not understand my struggles. I tried to explain to them what it was like to be me, but they didn't understand. It's not their fault, they never had to go through these kinds of things, so how could they understand? But I had to realize that there are some places these guys just AREN'T gonna wanna go.
That's my problem with most people, actually. I feel pretty comfortable telling it like it is, discussing what's surrounding us in our environment. Most people don't want that, they find it threatening that someone can be tuned into the world in a way that they can see most things that are going on, and people's hidden motivations. Most people want everything to seem like it's happy all the time, even if it's fake. I learned that very early on, and go with it, because I have to, but I know it's B.S. and I doubt I'm alone.
The best advice I can give you, I think, is remember that probably most people you know are naturally better at fitting in than you are. This is not necessarily a good thing for them, because the world is a pretty corrupt, fucked up place. But, they are going to see things more conventionally and on the surface than you will, because INFJs have an unusually rich inner life. Naturally, they fit in better. However, it is not a privilege that comes without cost.
Another possibility is that you might just not be happy in a smaller town. I wasn't either, that's why I got out of there. I thought there was something wrong with me for over 15 years because I couldn't fit in in a small town. Everyone was cut from the same mold; a different mold from mine. As you get out into the world, you can meet more people who are like you.
As for your friend, if she's a girl, she fits in better than you because she's a girl. They have it easier at the younger ages (which I'm assuming you are because you said you were in class). The problem is, women get the shaft in the long term, because once they hit 30 and our bullshit society sees them as "undesirable" because they've (God forbid) grown up a bit, fitting in becomes way harder for them, and so does finding a good man. It actually gets easier for guys as you get older, especially since we have such lower standards for looks compared to women...But I digress.
Also, if you're from a family full of introverts, be thankful, actually. I am from a family of extroverts. EVERYONE in my family is extroverted except my mother. It isn't as good as you'd think. Just sayin.
It felt good to write this, but, keep in mind I'm not saying anyone has to relate to any of this. It's my experience and no one else's, and I respect that.