I don't get this!

I don't understand. I do everything I can and for some reason I can't seem to do anything about my depression. I've had this problem for a very long time and it got worse around 2003 when I was in 6th grade. I thought everyone felt the way I did and didn't do much about it back then. But by 7th grade for some reason I felt like I was a bit different from people. I started to notice that I would get sad for no reason sometimes or just really mad. I could be having a nice day and then it just punches me in the face. I never understood it and still don't. I hate it and hate myself because of this. I've tried alot of different thing like talking to people, meditating, just crying it out and other things.
It only temporarily works if it works at all. But, then I always revert back the next day. I hate not being able to feel happy when I want. I feel like I'm a prisoner in my own body. Like someone else is always telling me how to feel. I don't like it, I should be able to control that myself. For some reason I can't and I really don't know why.
It's frustrating everyday when you wanna hang out with your family or friends and you don't know how you're gonna feel in the next 5 seconds. I try to just keep smiling and laughing, but somedays I can't even do that.
I hate it and hate myself so much for not being able to control my emotions properly.