Never good enough.. don't know what to do.?

I'm stuck in a huge rut... nothing I do is ever good enough for my parents! My mom has no emotional intelligence what so ever. Didn't finish high school, and doesn't know how to be a parent. I am just about to graduate and am almost a straight A student. My mother always finds things to cut deep at me for. We argue all the time and she will take it extremely far without question, even if we are in public. She would be quick to jump to conclusions like "just get the **** out then". I'm afraid to ask her even the simplest questions because she always snaps at me. If I don't help her out I will be totally screwed, but every time I ask to help her she always has a way to turn it negative by saying like "wow for once" "finally getting off your ***?". All I've ever wanted to be is a good person. But I have made so many mistakes in my life I think they may hate me forever. I got caught with weed, and my dad chewed me out so bad and pretty much said I don't mean **** to him. So there for I am afraid to defend myself of anything or be kicked out. I get yelled at for every tiny little mistake. And am really afraid of what will happen when I make a real mistake. I am forced to accept all the unjust comments and things that they do. They clearly favor my little sister and clearlyshow her so much more love than they do me. I feel just totally depressed because of my friends, family, and life as a whole. I want to kill myself. Pretty much all I do is read and work out to escape from my life. I feel as if my own intelligence is a burden on my life. I feel like I'm held to standards that are impossible to accomplish. I just want to have a normal life. I want something to fall back on. I've never been comforted on a day that I was sad. And almost every single day that I have been sad my mom chews me out for something and makes me feel like **** and so much worse. She makes fun of me for being sad? She always says "Awww do you feel picked on" she always wants to fight and she just yells all sorts of terrible things about me but she never has facts and details to back it up. It almost sounds immature and she can get away with saying whatever she wants and is always right because she is the parent. She is impossible to negotiate with. I am truly damned if I do and damned if I don't. If you took the care to read this then ANY help will do. I can't seem to get anything out of life.