I wonder if you're thinking too much about the bad things and stress. The less you think and ponder about it, the less it will affect you. I also think that sometimes, things will work better when you just relax and do what you enjoy and like, and not pressure yourself. Its more efficient that way , too.
I too don't think that you've bipolar. Its more likely that there's some thoughts that when invoked, cause you to fall out of your happy mood.
i'm sorry that you're having a tough time. but i think that if you will yourself and tell yourself " this, too.. is nothing i cannot overcome " then i believe that this is something that you will be able to beat.
I'm not really knowledgable regarding psychology and health but i do know that hard work, will power and a positive attitude will help you in virtually any situation. So keep that in mind .
If you need more advice or just a hug or a friend, i'll always be around.