How to fix my reputation?

Well, school finished and i'm going into 8th grade. 7th grade was hell. I used to be the small nice kid that most people liked. I had good friends and I was happy. But then this year i was the target of rumors and gossip. So many rumors about me spread this year and everyone thinks there true. For example, one of the ruomors was that i showed a girl my penis. No one looked at me the same way after that. The girl who i supposivly showed said that i did show her just for a few laughs but after that most of my friends stopped talking to me. All i hear is "ew!" when people see me. They always say to the girl "ew hes so ugly why would u let him do that hes gross" She keeps telling people she didnt want me to and i just did it anyway. People are SO mean to me now! The rumors started back in the begining of the year. Well i became depressed and started cutting myself and i told my best friend and he told everyone! For about 3 months all i was called was emo freak. Some person even went as far as taking all the stuff out of my backpack and filling it with cafeteria plastic knives. People would always get a plastic knife and pretend to cut their wrist and say "look! im joey!" They would laugh like its the funniest thing ever. For the last month of school no one would talk to me. Im not even kidding. It was terrible! No one wants to be seen with me now. I was hoping people would forget over the summer... but no. I heard a group of girls talking about me. They were all like "omg ew joeys so ugly he should go die. hes like a desperate freak no girl will ever like him" I just don't know what to do! The school knows about all this and they just say there just playing around. the school's doing nothing to help me and my parents dont care. My grades went from A's to C's from all this stress. How do i fix my reputation? I dont want to live through this for five more years.