I don't know if I can handle this anymore.

I don't understand the way I am sometimes. Somedays I'm fine and happy and other days I'm not. I understand what happens but I don't understand why it happens. It's been like this my whole life. I always thought it was a normal thing and everyone felt this way. But, then eventually during middle school I learned that it wasn't a normal everyday thing.
Anyway, I just hate being like this all the damn time. I feel like somethings got me on a short leash all the time just ready to yank me back whenever they want. I can't control anything. I wish I didn't have to isolate myself from people I talk to when I'm like this. I mainly do it so they won't get tired of me and so it won't be a hassle to them.
I've done everything I can about this. I've gone to doctors and done everything I could think of to control this. But, I don't know if I can take this anymore. I'm tired of randomly getting depressed for no reason and I'm tired of constantly being in physical pain all day every day.
I don't like complaining about stuff. I've been tryin to be ok. I've been trying to deal with this. But, it's too much and I'm starting to give up. I don't want to give up, but this is too much for me. I've been dealing with this my whole life basically and it stops me from doing things I enjoy and stops me from being around people I actually like to be around. It makes me a completely different person and I like being my normal happy self. But, it takes that part of me away for days or months sometimes.
I just want to be how I really am. I'm really just a happy and nice person. But, this depression makes me want to not be around anyone and makes me upset at every little thing and just does alot of horrible things to me. I'm tired of all this all the time every waking day of my life. I don't want to have to deal with this for another 30 years or 50 years or however long I'll be alive. I'm only 19 and I'm really tired of it now. I'm just so tired of this pain al the time.
I don't know what else to do. It's like my brain is silently screaming all the time for the pain to stop and I can't help my brain or my body. I'd love to help myself be relieved of this pain but I can't think of anything else to do. I can't fuckin think of anything else to do. I keep typing the same things over again, but I type journals the way it comes out of my mind.
I don't want to do anything severe to myself. The only thing I want is to make all of this pain stop. I don't know what not feeling pain even feels like. Everyday I'm always on the edge of banging my head against the wall or cutting off my legs to make the pain stop. And by on the edge, I mean any second I could do it. The only thing that stops me is if I fail then I'll have to spend alot of money in the hospital. And I don't have any money like that.
I just hope that something will happen. I'll try not to give up. But, I don't know how much longer I can do this.