Take a breath, friend. It sounds like you have many good things and many bad things in your life.
The first step is to let go. You have a brain that likes to think about things-- try to give your brain a vacation.
I noticed my life got a lot better when I decided I was just going to stop caring and stop thinking about some things.
For the things that really plague you, talk to a trusted friend or therapist. But, most of these thoughts won't plague you anymore if you find a guilty pleasure with which to occupy yourself for some time, be it food or sports or games or whatever.
Everyone has some little escape from the bad parts of life, find yours and just don't go overboard :)