Hey Elizabeth. :]
This boy probably knows you have low self esteem, and is using that as a target to get at you. Don't let him. I know it's hard but what he says does not
matter. Don't let him see that it's bothering you. Ignoring it and not rising to him could make him get bored and eventually he'll just leave you alone.
If he doesn't stop, say something to him. Tell him he's being immature and that it's not amusing anybody. Hopefully he'll realize that he's not getting anywhere by bullying you.
If he still doesn't stop, tell somebody you trust. Get an adult involved and I'm sure he'll back off.
Hang in there and PM
me any time you feel like it. :]