I sometimes also feel like you, even though I don't have anything to think negative about(I don't smoke, I don't drink, or whatever hurts your health).
Yet I also get in desperate shitholes. Nothing seems enjoyable. I don't feel like playing my favorite games, don't feel like watching TV, don't feel like eating my favorite things, and all that shit.
All you can do in those times, is wait it out.
I usually just go for a run or do some push ups and all that, or I start talking to everyone on facebook, even if I don't know them yet. Taking a shower or just watering your face with really cold water sometimes give me a wake up call.
I get irritated as fuck, but still, its better than nothing.
I even start thinking about suicide in those times(like how when you are dead, you have nothing to be worried about and all that bullshit pussy way to leave the world).
I geuss it is just puberty.
Good luck matey.