Little weight gain and ?s

Hey, so here is the deal, i'm a 22 year old guy, i'll be 23 in 5 months.
I'm 6', my weight varies anywhere between 135 and 145 depending on how I eat on any given day. I've never had a problem with the way I look, I mean i'm thin, but I never felt like that guy that you cringe at when he takes his shirt off. But recently Ive been thinking about putting on a few pounds and going for some defiition in my torso/arms area. I'm not concerned with getting huge, quite the opposite I dont want to be, but id love a defined 6-pack, and pecks big enough that my whole front part of my body isn't just flat, I figured whatever I have to do to accomplish that will beef my arms up enough to look proportionate and i'm good with that.
 
That being said, I have alot of problems with my stomach, I can't eat too much at once, or anything spicy, none of the good stuff basically. But unfortunantly my situation doesn't let me have a good meal in me every day, I end up eatting alot of fast food and diner crud. One of my main problems I think, is I don't know What type of food I should be eatting, so I can figured out what my stomach can and can not handle before I end up getting sick.
 
I also don't have any experience working out, nor do I have time to go to the gym. I go to school full time, have a full time job and also a part time job, plus a girlfriend, so I have very few spare hours every day.
 
So, what could I do at home, in my room to help my accomplish some of these goals? Using few or no weights would be best, i'm in no rush for tons of results right away, just want an idea of what I should be doing so I can start.
 
Also, what kind of foods should I be looking to eat on a daily basis?
 
Thanks alot everyone
-Steve-
 
p.s Can i post a picture of my body? Say neck to waist or something so everyone has a better idea of where I am starting from?

Pushups, pullups and situps are a great way in my opinion to get in great shape. Pushups for one can be performed almost anywhere in your house. I'd suggest finding the number of pushups you do until you feel at least some kind of burn, but aren't completely gassed out. Then i would do that nine more times; so you end up doing say 10-20 pushups; 10 times for a total of 100-200 pushups a day. Pullup bars can be bought at any sports store and can be installed pretty easily. I would do the situps the same way i said to do the pushups.