I too have found myself in a similar situation. I grew up on the farm and loved outdoors. I have always been pretty skinny but in shape. Now I moved for college and sit in a cubicle all day and then take 3 hour night classes, I have no time to make a decent meal in the day. At night I usually am starving when I get home so I grab fastfood or fix something fast. The interesting thing is I'm 6'5" and weigh 168 lbs. I've got a six pack still and eat fast food everyday. The thing I hate is how lazy I am now, I have a total lack of motivation from what I used to be. My grades in college are actually suffering too. I try and setup a plan to workout but it fails when the next week comes and I am swamped with school and other things going on. So even though I seem to be in good shape, I can tell a lot of things are out of whack lately...
I have a feeling that this unhealthy trend will catch up to me, but there's not a lot I can do to try and stop it, so I might be in your situation a few years from now... I just want to gain a little more muscle and keep it, sucks going back to the farm and just trying to keep up with your dad... lol
Good luck!