Ugh, I completely understand what you're saying. In in college right now, but I feel the same way... That I'm doomed to failure, and I can never really motivate myself to do better. I'm not sure why, but life is just so much better when I"m curled up in a ball hidden in my bed... I wish I had advice for you, some magic cure to make all us students suffering with depression or any other mental illness suddenly become straight A, over achievers with nothing to hold us back (which, I know, is how the rest of the world appears to us at times...).
Its funny, though, isn't it? When we tell people the way we felt at a certain time and they have no idea... My boyfriend and I went to high school together, but weren't really friends until the summer before college. He loved high school, so when I tell him how much I hated it and how miserable I was, he just doesn't get it. Especially since I "seemed fine."
Anyways, I'm just rambling, but I wanted you to know that there are others out there who have similar feelings to yours... I hope you can find a little peace and start feeling better.

Ro