Originally Posted by BrianMcG

The number one priority for you is to start eating large amounts of food, every day. Eat like every day is Thanksgiving. Eat at least 5 meals a day with a couple of protein shakes and you will be getting the calories you need.

Second stop doing so much cardio. Keep the cardio to no more than three days a week, 30 minutes tops. All that swimming you were doing is burning a ton of calories that could be used to build muscle. That is why you are so skinny.

Third Concentrate your lifting on these lifts:

Bench Press
Deadlift
Squat