You just need some time to yourself. When you think about all the mistakes you have made it the past just laugh about them. I mean you can't change them so why not make some fun out of it. But when I feel like that I just go in my room and listen to some music. Or I will just lay on my bed no tv, music, or anything on and just dream about where I want to end up with my life. That really gives me the boost of energy I need sometimes to get past the sad points in my life