Holy crap dude... Im having the exact same problem!
21yo, 5'11", I used to eat EVERYTHING and weigh around 140lbs, hard as a rock. Then I moved to WV. I've gained like 30lbs in like 4 months. I've never had wieght like this before and its freaking me out.
I've figured it out though. Im not currently riding dirtbikes. Back in Utah, I rode old dirtbikes and 3 wheelers like mad every chance I got. Motorcross is the 2nd most physically demanding sport in the world. (Soccer being #1)
If you ever see those guys AFTER a 15 minute race, they normally collapse in exhaustion. every single muscle in your body is FULLY tense continuously when riding FULL OUT
I dont have a bike right now, and thats why Im turning into butter (and all Im doing is sitting at the puter all day too!)
Get a bike dude... find some dirt to ride it, and ride hard a couple of hours a week.. the lbs will MELT off in no time, and its FUN!! Im desperatly trying to find a bike myself. Doesnt even need to be anything special. My last bike was a '74 yamaha DT360 that I paid $100 for.
P.S. If anybody in the mid ohio valley wants to get rid of a dirtbike for cheap. LEMME KNOW!!!!!!