Simply put, you need more quality calories. Also, if you have a fast metabolism, lay low on the cardio... Don't eliminate it, just cut it down....

As BillyBoy said, post what you are eating now, total cals, current weight, what your workouts look like, as far as how much cardio, sets and reps and rest periods with weights. If you are taking and hour and a half to do weights, you are doing something wrong. Maybe not intense enough, maybe doing cardio at the end, maybe overtraining... So lay it on us!