How to gain weight at 19?

hey erbody im 19 i weight 135 lbs i wanna eat alot but i dont really get hungry much and i dont need alot to get me full i smoke about a pack a cig week and like 8 blunts of weed a week i wanna gain weigt i weerk out and and ive tried taking the weight gainer but nuttin weerks what should i do