If you're looking to gain weight, it's just a matter of the right caloric math. You need to be taking in more calories than your body burns. If you hit a plateau, eat more. It's that simple. The muscles will come with the right workout/rest plans, and I would go a bit further by advising you to limit the cardio you do to just what's necessary.
On a 3000 calorie a day diet, I walk around at about 150-155lbs. I walk around right now around 185lbs with about 10% bodyfat at 5'11". It takes 4200 calories on a non-workout day and around 4800 calories on a day that I do workout, just to maintain 185lbs. I'm a skinny guy by nature, and if you're at all like me, you have to eat and eat and eat. Six meals a day, with a minimum of 700 calories each meal.