For your issue of gaining weight, there is a probabilty that you may have high metabolism:
Originally posted by another user
A high metabolism means that the body is burning calories at a greater rate than average. People with high metabolisms can generally eat more food without gaining additional weight which can sometimes be seen as a perk. For others who are forced to constantly consume large amounts of food on a daily basis to maintain their weight, a high metabolism might feel like a curse.
For gaining muscle, you're at a young age, therefore it would be a great age for building muscle as your muscles would generally recover faster and build up more efficiently.
For muscle building I would suggest go heavy (and I mean heavy) weights and low reps (amount of lifts, pulls, etc).
For building body energy, stick to low weights and high reps.
Drinking protein shakes will help your muscles recover faster from soreness. If you have never been sore before, understand that the first time is always a bitch but you will eventually develop to it.