when i was a kid i would barely eat anything and i would get full fast. i was a very skinny kid. if you are struggling with mass you need to eat more.. the trick is don't eat foods that fill you up and avoid condiments. eat healthy whole foods and lay off dairy which upsets the stomach where you won't want to eat
I dont like feeling full as I usually get tired that way. I eat smaller meals that still make me feel light. I avoid red meats as it requires alot of energy to digest it!