Clinically depressed at a young age?

I'm 16 years old and I Think I might be clinically depressed. A lot of people tell me its hormones but I really think it's more than that. My mom and her parents both have depression and I believe they're all on zoloft. I've had major weight fluctuations in the past two years, I feel worthless all the time, and lonely and when I think ONE thing is going to make me feel better it doesn't. My grades have slipped a ton. I have tried to commit suicide before (twice). I just feel like everybody is going to surpass me in life, all my friends, siblings. And I'm going to be nothing, and do nothing. My parents have told me that before too. Someone please help me? :( I don't know what to do anymore and it's scaring me. I don't want to bother talking to my parents because I don't want to be a burden to them. And I'm not trying to be dramatic I'm just really, really lost.