I know it sounds trite, but if you haven't I really recommend taking up some kind of exercise. It's frankly amazing how fast my general attitude turned around when I started swimming a few hours a week. The malaise I'd been living in since I was a teenager evaporated in a few days, and I was like a completely new person. Every so often I'll get a little lazy and not go for a bit, and the stupefying brain fog of depression always serves as a pointed reminder.