Really brave of you to make your first post.
First thing I want to assure you of is that your post and the way you are feeling is not at all "dramatic", your feelings are completely valid I promise.
I read your post and I really felt for you, It was like reading my own mind thoughts from highschool. I am 32 now but I vividly remember those days in high school and through to college. I had one friend but our classes didn't always align well so I would sometimes be on my own, which I couldn't handle. I used to eat my lunch in a toilet cubicle because I was terrified of people looking at me. Also spent a lot of time in the library - massive safe haven (thank you library!).
It can be really really really hard when the people you feel like the people you are sitting with don't want you there. I know that I can't judge for certain what anyone thinks, but I do know from my experiences and finding out various things from my own situations that people weren't actually thinking what I thought they were and in some cases I had misconstrued what they had meant because I took their words in a different way. It was my own head trying to put me down and the anxiety monster trying to grow stronger.
It sounds like some of those people have really put you down and made you feel unaccepted, which is not ok at all.
If I could suggest anything to high school/college self it would be to take a big deep breath and tell somebody that you trust about how your feeling, and not just like a casual thing but take just one person aside and say "hey i really need someone to talk to, can I talk to you?" -maybe even your parents if you feel you could trust them the most? They could help set up a doctor appointment for you which could lead to getting some assistance with getting through your anxiety - the sooner you ask for help will make the world of difference in the long run.
High school is tough, really tough, but you made it half way already, you can do the rest :)
I hope you are getting through today more easily. Take care.