Sounds like you don't take in a lot of calories and you may or may not have a high metabolism
Eat a lot of things like: brown rice, whole wheat bread, peanut butter, nuts, sweet potatoes, milk...all are healthy foods that are calorie dense
Count your calories and macros! If you aren't one of those people who just naturally eats the right amounts you have to count, there's no other way.
I have a high metabolism and I always post my fitday account when people think they are eating a lot. I'm currently maintaining:
Word. I couldn't agree more. It works both ways. Typically, when people want to lose weight but aren't tracking calories, they find that they are eating too much, and when people want to gain weight, they simply aren't eating enough. Keeping track of calories really gives you an idea of how energy works, and what foods pack a punch. Tracking cals is a must, if at least until you become familiar with the numbers and whatnot.
For example, I was shocked the first time I measured out 28 grams of peanut butter, which is 190 calories, it was barely anything! On the other hand, 2 heaping cups of carrots and cucumber is 50-60 calories...
Seems like common sense to some, but most have no idea what they are putting in their mouths...