ANDY'S ANSWER: Some things you can do is avoid situations where you are alone with the girls that are tormenting you. Come earlier to class, leave the class a little later, spend breaks in the library or somewhere other than where these girls normally hang out, etc.
Make friends with someone else that you can walk with and get moral support from. If there is others that are being bullied, ask if they want to hang together with you and you can stick up for one another.
According to bullying.org, bullying stops in less than 10 seconds 57% of the time if a peer stands up for the victim.
Bullies depend on you being too intimidated to say anything to an adult, so if you don't tell, your school can't do anything to help you and other victims. Document the incidences with the bullies and then talk to your school counselor or your principal.