Your dominant function is Fi (Introverted Feeling). It looks at everything in terms of morals and values. It causes you to live inside your head, and it turns even small decisions into big moral battles over what's right vs. wrong, what's fake vs. real, what's "you" vs. "not you," etc.
It also tends to give off a sense of anxiety or even impending doom at times of high stress or personal (internal) conflict. NFs in general feel it for various reasons, but the INFP version can be particularly toxic. The INFP version can come on strongest precisely when you should be happiest and enjoying your successes. Here are some quotes from the experts concerning INFP anxiety:
From "Type Talk" by Kroeger & Thuesen describing the kind of pressure INFPs might find themselves under:
From Keirsey's "Please Understand Me":"The potential for self-doubt and self-criticism is always close to the surface. Even when told they have done a "good job," INFPs know the only true judge is themselves, and may punish themselves for work they consider less than perfect. In general, while INFPs love to learn, grow, excel, and please others, they are always their own worst critics; they often remind themselves that they could have done better. It is a lifelong struggle between self-approbation and self-depreciation. In the end, INFPs almost always tend to sell themselves short."
As far how to address the problem and achieve what you want: Watch people who are doing what you want to do, study them closely, and then mimic them. Basically, you want to bypass your Fi (at least for purposes of doing new things) and engage your auxiliary function of Ne (extraverted Intuition). You want to bypass the big internal debates about who you are and whether a certain role suits who you are, and instead just study how others do things and then throw yourself into the same experience.Even at the best of times, they seem fearful of too much marital bliss, afraid that current happiness may have to be paid for with later sacrifices. The devil is sure to get his due if one experiences too freely of happiness, or, for that matter, of success, or beauty, or wealth, or knowledge. This almost preconscious conviction that pleasure must be paid for with pain can cause a sense of uneasiness in INFPs when they marry; they may feel they must be ever-vigilant against invasion, and can therefore have trouble relaxing in the happiness of mating."
So sign up for things and throw yourself into new activities. You want to get outside your head and engage in activities that force you to engage your extraverted auxiliary.
Don't hold off doing things until they "feel" right, because you'll just end up waiting forever. Instead, disregard your "feeling" Fi function and force yourself to get good at your auxiliary Ne function by throwing yourself into extraverted situations. You may not extravert brilliantly at first; you may extravert for a bit and then need to retreat back into your head to recharge. You may go through cycles of expanding out into the world and then retreating back into your head. But once you've recharged inside your head, then pick a new extraverted activity and try again. Just study others and do and say the same things that they do and say until your comfort level increases.
And don't be afraid to fail publicly at times. Sometimes it takes a couple times to get things right. So get used to taking some public pratfalls and playing the clown for others until you get it right. That's just part of living the extraverted life.
As for that buzz of anxiety or impending doom, just tune it out as background static. It's a false signal; it's not a sign of any real danger. Shove it into the background enough times, and eventually it will fade over time.
You’re a 17 year old INFP. I'm a 51 year old INFP. When I was 17, I left home with $50 in my pocket and hitchhiked cross-country. I found a job in the city as a janitor at a YMCA, and soon after my 18th birthday I joined the Marines. Soon after my 19th birthday I was floating off the coast of Vietnam for the fall of Saigon.
I've traveled around the world, went on a college exchange to Leningrad before the fall of the Soviet Union, have been trained and registered with three scuba diving organizations, have done about 40 parachute jumps, had many loves and two wives, speak a couple languages, am pretty good at ballroom and latin dancing, etc.
You don't have to live your life in your head if you don't want. Fi is your starting base, and retreating inside your head is your comfort zone. But you can learn to venture outside your comfort zone for longer and longer periods and get good at other things too. I always just figured that if other people could do things and survive, then I should be able to do them as well. I just put aside the internal moral debates and the anxiety, watched closely how other people did the things I wanted to do, figured I was no worse than them, and went for it.
The Roman playwright Lucretius said: "I am human; nothing human is alien to me." Basically it's just a fancy way of saying "If other people can do it, so can I."