How can I continue with my life as a boy who doesn't know?

I have a dilemma. I'm now 17 years old and a junior in high school. My childhood is comprised of being beaten constantly, witnessing death, and never understanding. I was attending public schools and of course they were what they were, but I was in a wheel chair 7th and 8th grade after having my knee dislocated 6 times by students. My teen-hood is pretty much getting into the high school of my dreams through hard work and determination (4th best school is state) , being the odd one out (going to public schools all my life,growing up surrounded by "the hood", and being 1 of 4 black people at my school. I arrived there and got strait C's and F's my freshman and sopre years because of my secret depression that i've kept to myself for 3 years. I lived by myself in an apartment an hour away from my school most of freshman year, I never did drugs or cut or anything of the sort. Junior year is alot better, but as always something seems to be holding me back. My mom tells me that she is considering pulling me out of the school after Christmas (great present right?), and she used to threaten me with it before, and I can't seem to put effort forth when I don't know where I'll be. I don't like to complain, and I try to stay optimistic, but.. I can't do it forever. No one understands me really, but at this point I don't think having no one there for me in my life is something that isn't second nature to me. Ofcourse I have low self esteem, but I can't seem to open up fully. Im getting A's and B's and 1 C in school now, because of the releif of being able to come back to the school (after being constantly bombarded with threats before) but it's happening again. How can I continue trying and feeling like I am. My past haunts me rarely, and I've come a long way by myself. What do I do?