I can't take this anymore ?

I'm having a really hard time dealing with life right now and I need advice. I have social anxiety disorder and being in any kind of social situation is torture to me. I constantly feel that everyone is judging me for the way i look and the things that I say. I want to be able to have social relationships but I am not able to. School is hell. I feel like a complete freak and outcast and barely talk at all throughout the day. On top of all of this I constantly think about my weight and apperance. My sister was an anorexic and would call me tub *** and lard ball all day long, my mother didn't exactly disagree with her. I ve lost weight and am now an average girl, but I have a mind of an anorexic girl without the willpower to starve myself. I have almost no desire to live Anymore. And I don't know what to do