From reading your other posts, it sounds like your parents are pretty focused on your sister right now. They need to be made aware of just how much you are hurting, and I know you have tried to tell them, but something isn't getting through to them. I would get another adult involved. Someone they can't simply write off and say you're "hormonal". You need to somehow make it to school and go straight to the guidance counselor's office. Tell them what's going on. Be totally honest with them and don't downplay things. You're not seeking attention. Ask the counselor to bring your parents in and have a talk with them. Once the school is involved, they will likely be watching to make sure you're getting treatment.

A guidance counselor saved my life when I was your age. They can help, but you need to let them know you're hurting.