Woah, em-- No, not even going to go there for a joke this time.
First off, congrats on winning the fight of not smoking. You're too young anyway. Don't give me reasoning either, smoking kills you either way.
At any rate, it sounds like maybe you've done what I did a long time ago. See, I was the kind of kid that you are now. I was a mostly passive kind of guy, I didn't really let stuff get to me... sure I'd give my opinion and tell them what I thought once in a while, but for the most part, it didn't effect me...
What I didn't know, is that no matter what you do, it still builds up inside. Think of it like a dam -- sure you stop the water, but a little is going to get past every time. That example aside, one day, it all finally came out. Me (I was 12 at the time) and my 16-year-old cousin (who weighed like 190 lbs, about 6'3) were rough-housing around, and I was starting to get annoyed by it because I didn't want to do it anymore. Well, around that point, he tried to DDT me and I ended up smacking my head into the wall.
It clicked.
It basically set off this bomb that had built up over the years. I just snapped, and next thing I knew, my parents and his parents were in there pulling me off of him, because I was choking the life out of him. To this day, he still talks differently.
It sounds like you have a build up of pressure. For some people, taking walks and shit like that won't work. You have to find that medium in which to express your emotions. That's why some people resort to self-abuse: it lets them express their feelings in a way that someone will notice -- themselves.
At least, that's what kind of problem it sounds like to me. You need to just find a way to channel all this. I know I sound like some kind of psycho-quack, but it does work when you find the right way. Hell, also, it would help if you actually took a more active stance once in a while, instead of a passive one. It keeps it from building up.
If this doesn't help, gladly PM me. Hope it does though.