I'm depressed and I hate my life?

I'm 17 years old and I feel like I'm on the edge now. Basically, I've always had problems mentally. I was bullied from childhood and I had counselling to help my self-esteem. But when I turned 15 I finally grew a tough skin and the bullying doesn't bother me now. I'm about to enter my final year of school but now I'm having problems with depression, and it's been going on for years. My family have never understood me as I'm different, unlike them I am strongly religious and I have my own philosophy and passions. My dad is insulting and has a split personality. He's nice around friends but really horrible to me, he takes out all his work stress on me. Then he tries to be nice for a few days, but after that he goes back to his usual self, he also never listens and always thinks about himself. My mum understands me to an extent, I'm definitely closest with her. But she never sticks up for me and I think she wishes that I was a "normal teenager", as I have "weird" philosophy compared to her. For example, I won't date till I'm 18 as I don't think teenage relationships work and are a waste of time and I also believe in not having sex before marriage. She thinks these rules are strange and doesn't listen to me. My brother is at university so he doesn't live with us but when he's at home I hate it even more. He always takes the opportunity to correct me or better me in an argument to prove he's cleverer than me, he compares us in so many different ways that it lowers my confidence and makes me think horrible things. He really doesn't care about anyone but himself, he obviously gets it from my Dad. I have a lot of friends but they never seem to understand me as I have different interests to them. I also act differently around them so they don't know what's going on. My depression gets worse every time I think negatively, I hit myself, I call myself ugly and fat, I make myself sick, I tell myself that I'll never get married as no one will ever love me etc. It's gotten to the point where I've tried to kill myself a few times by taking an overdose of painkillers. My mum has hidden the painkillers now. I get so angry that I freak out and break things and cry in my room for hours. I just want to die or escape this small town in England that I hate so much. I may be going to university next year but i doubt it'll happen considering how stupid I am. When I'm at my friends houses I usually go into the bathroom and cry because I wish I had parents like them.

I don't know what to do anymore, the only thing that helps me is songwriting. I'm in so much pain and I'm on the brink.