TeenHealthFX wants you to know that there is help for you. You are right - your classmates have abused you and that needs to stop now. Schools are now beginning to recognize that bullying is not an innocent phase that every person experiences, but an abusive behavior that needs attention. Schools have an obligation to protect all their students from bullying or any other abusive behavior.
You do not say if your parents are aware of what has been happening to you. Talk to them about what is going on and what the effect of this kind of behavior is having on you. Have them talk to the administration at your school to let them know that the behavior has to stop. It is your legal right to have a safe education.
You also need to tell your parents about how extreme your stress is and your avoidance of school and how your grades have fallen. They are probably already aware that you are having some difficulties.