Hey man, maybe i can help you out.
I've done martial arts my whole life but my whole life I have been cursed with a small frame and a metabolism from hell. I eat like a sweaty fat man at an all you can eat buffet on a daily basis. But still, i gain maybe 1 lb in a month this way. If I skip a night of dinner (or forget, or am too busy, or whatever) I'll lose a lb or two. My metabolism really sucks. Anyways, about 2 years ago I weighed in a pathetic 135lbs. I'm 5'8 so thats TINY.
Today I am 160 - 165lbs natural and have stabilized my weight, although Im having more trouble getting over 165 now too. The way i did it was with a moderate workout schedule. 4 days a week of heavy and light lifting maybe 45 minutes each day. My fav is doing sit ups with a 50lb dumbbell in each hand. Anyways, I drink a creatine shake as soon as I wake up everyday, have a good breakfast/lunch/dinner + a protein shake and maybe a protein bar to snack on later. I'll drink another creatine shake and protein shake before I work out (on the days I do so).
I dont buy the cheap crap or the real expensive crap, just read the labels and get the best mix of what you want. I would have never gained 30 lbs in the past 2 years if i didn't drink the creatine and protein shakes (on top of a calorie heavy diet) even with exercise because I exercised even more when Iw as still 135.