Too tiny

I am fifteen and most girls my age have nice bodies. They don't have thigh gaps and are pretty. People look at me and call me anorexiant and tell me to just go ahead and kill myself. Starve go ahead nobody cares. Someone pointed out they could see my rib cage when I went swimming and told me I was ugly. My boyfriend saw this as I grabbed a towel and put around my waist. He told me to come over where he was at and he took my towel, put his arm around me and told me he didn't care. I was pretty fat or small as a stick. So I have started eating more and it hurts. My parents don't understand and try to shove food into me. What can I do?