Kayleigh,
You sound like me to a tee. I go through the same things that you do. Everything is fine until one thing goes wrong and then forget it everything sucks. It is the depression talking. We tend to walk on a tentative edge as it is that only requires one upset to cause us to fall down. You are not alone (although that might not help). Try to be strong and just pick yourself up as much as possible when it happens.
The only thing that seems to help me is when I keep on going and try to keep as busy as possible. This way I do not think about these things as much.

Take care,
Jessica