I think the problem is not so much how often you eat (eating often is healthful), but what you're putting in your mouth when you do. You need to eat better foods- the less processed the better. You are on the underweight side (I assume...I don't know how old you are or how tall), but so was I until I was in my late 20's. Eating complex carbs with a good balance of protein/carbs/fat/fiber will help.