Feel like I'm trapped in a meaningless life. How do I stop feeling like this?

I'm trying to be brief so this might be a bit confusing. And I may seem like I'm whining, but I'm not, I just want to feel better...

I'm a 15 year old girl in my last year of school. I've always been seen as shy, even though I say whatever comes into my head when ever it comes into my head. I have a few friends, but no best friend or even close friends. I don't have many thoughts and I don't know how to be myself around people, even though I try my hardest.

For the past year I've felt completely trapped in my life. I get good grades at school (all As and A*s) and I know that I'm gonna have lots of carreer oportunities in life. But I just feel as if whatever I do with my life, it will still be meaningless. I try to avoid social situations, even though I know it's bad for me, but it's because when I'm out with my 'friends' I just feel even more depressed that I can't be myself around them.

I'm very introverted. I never tell anyone how bad I feel because I don't want to burden them. I never cry, I haven't for over a year. I don't feel anything anymore. I don't get upset or happy, I don't laugh. I don't get angry at people, but when I'm alone I get over the top angry for no reason at all. Like I'll punch my wall just because it's there. It's like an overwhelming sense of helplessness. The only emotions I feel anymore are that strange kind of anger/frustration, and the sense of helplessness. The feeling that no matter what I do with my life, I'm still not gonna feel good and be happy.

I self harm, I've never told anyone because I feel like that would be attention seeking and self absorbed. I do it because I just want to feel again. At least when I cut I can feel pain, rather than this sense of numb hopelessness. I also crave adrenalin. I wish for an adrenalin filled life of excitement that I know I'll never have. When I cut, I get the rush of adrenalin I crave so badly. But I'm not suicidal. I'm grateful for my life, more grateful than you can imagine, and I know that by killing myself nothing would be achieved and it would just make everything worse.

I often think of running away and starting over. Living a life of crime in hope that it will help me to feel again. Anything other than the hopelessness I feel now. I live with my mum, step dad, and 13 year old brother. My brother dispises me. He treats me like **** and always puts me down and makes fun of me for being shy. My stepdad is an asshole although he pretends to be nice. I love my mum, but I can't talk to her about anything or be myself with her. My dad, who I barely ever see, used to abuse me verbally and emotionally. And isolated me from everyone. Sometimes even physically. I know it seems strange but I miss those times. At least then I had some excitement in my life. Trying to fight for survival. I used to have councilliling when I was about 9 because my dad was sent to prison but I didn't want to speak to the counciller about myself because I felt as if it would be self absorbed and self centered to do that.

I really hate feeling like this, but I don't know how to stop. I want to be happy and optamistic like I used to be. I don't know how to be myself. I don't know what my personality is like. When I'm with people, I don't habe any thoughts in my head. I can't say anything because there's nothing there to say. I can't even speak to my own family. I barely say a word around my aunties/uncles/cousins etc, even though I try my hardest. I just dont know how.

How do I stop feeling like this? And why do I feel this way?

If anyone bothered to read that, then thank you, and I'm sorry it's so long. I must sound so selfish and whiney but I don't mean to. Please help me if you can, I hate feeling like this.....

Please and Thankyou.