I am the same exact way! It drives me freakin nuts! I have had type 1 diabetes for 16 years now and I have the worst anxiety and depression sometimes and then all of a sudden I'll be totally bi-polar and I'll be perfectly fine. I'm actually going to talk to a counselor about it because it has gotten so bad. I had a panic attack in my car once when I was driving and I almost crashed. So my advice, definately talk to someone about it because talking about your problems literally will help alot. Don't keep your feelings couped up inside because at one point it will finally explode, which is exactly what happened to me.
And yes, alot of it probably has to do with that fact that your a teenager and high school can be very difficult and extremely overwhelming especially if you are a diabetic. But if you think your alone, your not. Everyone feels the same way no matter what you think. Everyone your age is self-conscious and feels horrible about themselves at one point, but your a teenager and your supposed to feel that way because your developing into an adult and your hormones are raging and things are changing and its just hard.
I really hope it gets better because I know how you feel and its not fun :(
I think that as a diabetic I am a lot more aware of my body and can get more paranoid then most people. But also a lot of it is age and being a girl to. With diabetes I find that if my blood sugars are out of wack then I freak out more over little things.