I'm in the Same situation. Some people like to sit down and study. Even for the rest of their lives. Some people don't.

When I was a kid I always studied well because if I didn't, I couldn't go outside. Try rewarding yourself. You may be like myself with self defeating personality disorder where I fail by not trying or even on purpose to the point where I set myself low personal standards and fail to achieve them.. It's sad. If you want to succeed in life, think positively. (helping others and not helping myself is also a part of it..)