Hello~The teen years are full of changes, and the hormones are one of them. Having flucutating hormones can cause all kinds of "icky" feelings, and anxiety and feeling weird are a few of them.
If you have not seen a good gyn or family doctor, I would suggest you do so, they can run some tests and take a health history and be able to help you get a plan of action going.
It's almost undoubtedly just a phase of life. Teenagers have a lot of ability but not a lot of chances to do real stuff with life-and-death consequences (in our culture anyway), and that's not always such a good thing (even though we design our culture this way to protect kids from bad decisions). The reason it's not such a great thing is that it doesn't give you enough important to do. Then you get self aware and worry and stuff. Try something serious, like volunteering at an interesting charity and throwing yourself into it. The activity will help and will give you bigger problems to think about too.