Illness sucks

Hiya. I'm a girl at secondary school in y9 and a boy in my form keeps calling me mean names and saying mean things about my hair and and my eyebrows...a bit ago I lost hair from my eyebrows cos I'm not to well and my hair is very thick so I'm alright but it is getting thinner which means more greasy and stuff but he won't shut up about it I tried to explain this to him and he says he doesn't care and hopes I get worse. How do I handle him I feel as if I can't move on he's pulled me down so low I can't help being ill. I wish I could find away to get rid of him or say something back but many people back him up.  I sit next to him in a few lessons and I can't escape him! Someone please help.