I have told my mum, but she hasn't done anything:(?

Sounds like an infection. You need to see a doctor. Your mother might not understand this. Ask her if she can take you to the doctor. If she won't, tell the school nurse. That's what the nurse is there for. It might be a little embarrassing, but it's necessary in order to be cured. The nurse will call your mother and tell her that she needs to take you to the doctor. Your mother will listen to the nurse because she'll get in trouble if she doesn't.