Protein shakes and bars work well- they are often used by wrestlers and stuff.
Try eating 5 small meals a day instead of three large meals and just eat what you want. However, make sure you eat your fruits and veggies and get carbs and protein too- not just junk food.
Exercising may make you more hungry and cause you to eat more- that might help.
Just stay healthy...That's the key. Eat healthy, exercise, snack, etc.
Take care...Bye.