Hi all-

This community looks a lot nicer than some others I was poking at, so I figured I'll ask my question here.

I've been working out regularly since college. For the last year, I've been getting in between 3-6 workouts a week, every week, without fail. Right now, my schedule (on a good week) is like this:
Sunday - Yoga & (sometimes) cardio - sometimes legs
Monday - Upper body
Tuesday - Legs
Wednesday - Boxing - sometimes upper body
Thursday - Cardio & legs
Friday - Upper body
Saturday - Martial Arts

Right now, the only cardio I'm really getting is in boxing and martial arts. When it warms up, I'll be running outside again, hopefully at least 3x a week.
I do abs with every upper body or leg workout.
Leg workout is usually machines after a mile run.
Right now upper body involves a ton of pullups (60-70), pushups (75-90), and dips (90-100) because it's too cold to walk to the real gym and there's one in my building (but the heaviest weights are 30 lbs - yeah okay).

I'm in good shape, some people tell me I'm in great shape. You know how it is, though, always something more to strive for.

I'm 5'7" and about 145, last I checked. So, my BMI is pretty much perfect (I think I'm technically 3 pounds underweight) and my body fat is just about non-existent. That's great and all, but I've never been happy with my size. I'm the second-youngest of my generation and most of my older cousins are these hulking guys. I didn't get that gene.
The thing is, I can (and do) out eat them, as well as almost everyone else. I eat a LOT, but I just don't seem to put on weight. Other than saying "eat more," anyone have tips on what I could change? I'd really like to be stockier. Not sure exactly how much weight I'd like to put on. Maybe 10-15 pounds, because of my height.

My eating habits are something like this:
8 AM - Peanut Butter sandwich (whole wheat bread)
9:30-10 AM - Apple or some kind of fruit
11-12 - Sometimes a banana or some almonds
12-1 - Lunch (Usually chicken and rice / potatoes or pasta with meatballs, sometimes sushi or a burger, depending on if a rep is taking us out)
3-4 - Banana
6 - PB&J sandwich
7-8 - Dinner (Again, usually chicken and rice / potatoes or pasta with meatballs - Don't judge me: I'm a single dude, I cook for myself!!)
10-11 - Sometimes some fruit

I try to mix in protein shakes (muscle milk) from time to time, but not every day. Too expensive. When I can find liquid flax seed, I mix that in.
I NEVER eat fast food, I almost never eat any candy or junk food. I don't drink coffee, but I do drink a lot of tea (usually decaf green / red).

Again, sorry this is so long and thanks very much for the help! Been working up the nerve to just ask this for a long time.