It could be a lot of different things.

the unifying thread of all your anxieties is very simple, though.

You KNOW how you SHOULD feel and when you do not feel the way you think you SHOULD, you panic.

This is not really living a life. This is more like rehearsing or practicing or taking a peak at what life MIGHT offer.

Your life is in flux and that is age appropriate for you. That you question things intellectually is also age appropriate for you, and in general a good thing to do.

The bad thing for you is censoring how you feel. Life, with all its surprises, begins when you stop censoring how you feel or telling yourself how you should feel, but actually feel something.

For right now, cease being a censor of your feelings and attitudes and take the position of an observer. Notice how you feel without any type of judgment whatsoever. Just notice. That would be the beginning of actually living for you.