Gaining weight = Calories in > Calories Out
Eat more than you expend, period. Get a weightgainer shake, I use CytoGainer and it's helped, I was 6' 156 now about 170 after a couple months.
DO SQUATS! the muscles in the legs are the largest and will see the greatest gains the quickest and it stimulates anabolic growth within other muscles thruout the body. You don't have to work out a lot during a week, since you dont like to work out, develop a 3 day routine, MWF, and make it a full body workout with core lifts each day. Like reg. bench monday, DB Incline Wed, reg. DB Friday, stuff like that.
Also, just doing push ups throughout the day will help your chest a lot (more than you would think) and a pull up bar in your room is a good investment, just always do push ups and pull ups whenever you find the time.