We all know that bullying goes on in every school but it's the way it's dealt with which makes the difference between life being tolerable or a misery. Bullies are very cunning and are expert at getting away with it.
If you are being bullied, tell a friend, tell a teacher and tell your parents. It won't stop unless you do. It can be hard to do this so if you don't feel you can do it in person it might be easier to write a note to your parents explaining how you feel, or perhaps confide in someone outside the immediate family, like a grandparent, aunt, uncle or cousin and ask them to help you tell your parents what's going on.
Your form tutor needs to know what is going on so try to find a time to tell him/her when it won't be noticeable. You could stay behind on the pretext of needing help with some work. If you don't feel you can do that, then go to the medical room and speak to the school nurse.