I think I have social anxiety. At home, I would be myself. Outside, especially school, I'm always anxious. I always have this shortness of breath feeling, like, even though h'm breathing, I'm not getting enough air. I find my chest very tense and my head always feel out of order. I'm always thinking how to act, and I can't seem to concentrate on anything else. When I talk, I always repeat what I said in my my head to see if it sounds "okay".

My chest always feel very tight and tense. I can't think, can't concentrate, and most of all, I can't express myself openly. I feel like I'm locked up in my own mind, always talking in my mind instead of saying it out.

I really need to stop this. It's taking over my happiness and all my friends. I have nothing to talk about so now, most of my friends think something's is wrong with me and that I'm boring. I even feel it. I'm boring.

It only happens at school and sometimes in public. Not at home. I feel insecure in public.

Could be a social anxiety disorder. Maybe you should see a doctor and tell them about it. Or, you could just be at that age where everything is awkward and weird. Maybe go and talk to your school counselor and tell them how you feel. They're there to help you sort out your problems and they might have more ideas as to what it could be.

Just be yourself, I'm sure you're not boring at all!

could be a social anxiety disorder. Maybe you should see a doctor and tell them about it. Or, you could just be at that age where everything is awkward and weird. Maybe go and talk to your school counselor and tell them how you feel. They're there to help you sort out your problems and they might have more ideas as to what it could be.

Just be yourself, I'm sure you're not boring at all!

But the problem is, don't want to let anyone know.

Yes that does tend to be an issue.
However, school counselors I believe are subjected to privacy laws, and if not them I think if you go to see a doctor on your own they won't be able to tell your parents (but I'm not really sure what the privacy laws with that are).