coming from someone who had it big time during GCSE year, that sounds like anxiety. it's not easy to deal with, and even worse if you don't have your parents' support, but I can say a few things that helped me out.
1. when you're feeling anxious, the most important thing is to very carefully analyse exactly what's making you anxious and why. what is it about going to school or answering questions that makes you anxious?
here's an example train of thought:
why am I afraid to get called on in class? -> because I'm afraid that I won't know the answer.
why am I afraid of not knowing the answer? -> because I'm worried that my classmates will judge me.
why do I care about their opinion of me? -> etc etc.
anxiety tends to have you catastrophising a lot. when you break down your train of thought into very logical steps and consider what you're afraid will happen vs what's likely to happen, how bad the worst case scenario really is, that sort of thing, it seems a lot less extreme and easier to manage.
2. it sounds from your post like you're more anxious about the social aspect of school than the academic aspect, although maybe I'm misreading that. social anxiety is a b-word, but the best thing for me was a) to realise that my peers aren't actually focused on picking apart everything I do wrong, and that b) their opinion of me doesn't actually matter. which is easier said than done, obviously, but it helps to consider the fact that two years from now you won't see them ever again and it won't matter what they thought of you.
3. if crowds at break/lunch make you anxious, it's easy to redirect yourself away from them. I spent all of my lunchtimes in different classrooms doing extra work during my GCSE year - which meant that I had more time to study, and that I didn't have to be in the lunch hall, so it killed two birds with one stone.
Let me know if there are more specific things making you anxious and maybe I can give more advice.