Eat more often and make sure that you don't eat unhealthy.
Also eat as healthy as possible and have at least 6 meals a day and healthy snacks.
Your meals might look like this
* Breakfast - omelet with bacon, cheese, tomatoes and mushrooms
* Protein shake
* Small meal #1 - 5 Provitas/other crackers (make sure it's whole-wheat with fat free cottage cheese, tomatoes and cucumber
* Lunch - Pita bread with chicken breast, tomatoes, lettuce, cucumber, fat free cottage cheese and sweet chili sauce
*Protein shake after gym
* Dinner - Grilled salmon steak (100 g), 6 baby potatoes, green beans and mixed salad
* Dessert: Fruit salad and custard made with reduced fat milk
* Protein shake before bed
Healthy snacks that you should include are:
Weight training is excellent for building muscle and as muscle weighs more than fat, you are sure to pick up weight. But not unhealthy weight from fat, you will get lean muscle mass.
Protein shakes in-between your meals will help you to build muscle. Drink one in the morning, one after gym and one in the evenings.
Hope I could help, Good luck!