Never ever give up!
You're doing great because you're making something out of yourself, and even though it gets tough for you, just keep on in there.
I can recognize everything you're feeling right now because I've been there myself. We are just as young you and me, and keeping up with all these is not easy.
Go out and search for other jobs/or second job at your spare time, try to find something better than what you got now. I had 3 jobs at a moment just to keep up with rents, and everything else that I wanted. So never give up, go out and search and search, show your ambition!
Put out your goals, and go out and hunt for them!
Never stop believing in yourself!
This helped me alot, I watched it every day when I woke up.
Maybe it can do the same for you!
http://www.youtube.com/watch?v=pH3QZvBfZeY