I'm sorry you're going through this.
I would encourage you to talk to your parents or an adult you trust about this. I think a visit to your doctor for a check up is in order.
Best wishes to you - lots of good help here on this forum, feel free to keep asking questions!
Sounds exactly like nerves. Nothing else. This can be corrected. And you are so young, this can be corrected SUPER easily if you find a good talk therapist and or psychologist.
You don't need to fear about taking medication. At your age, most Dr's wont even think about putting a teen on medication for anxiety. So don't start fearing silly things like that.
The most important thing you can do is tell your parents, and they can help you talk to someone and get it under control. You are so young. You can and will overcome this I'm sure of it. ;)
You've already stated above this started when you began a new school. You've just picked up some nervous habits that are unpleasant. The good news, you can UNLEARN these habits with the right kind of talk therapy. Best wishes to you. :)
Anxiety can not harm you. :) It can be unpleasant. And again, you can unlearn this if you talk to someone sooner than later. God Bless you! :)