[rpmcduff]

Fatcapnap has excellent suggestions above. If you are looking to gain weight you are really looking to gain muscle not bodyfat. To do that you need to do weight/resistance training. You said you had trouble lifting heavy weights at the gym. You need to lift heavy for YOU, don't compare yourself to others. Lift weights that allow only 8 repetitions before you can't do another or your form suffers (this is called failure). 8 repetitions have been shown to build strength the fastest. (6 reps build mass fastest, 10+ build endurance.) After you have gained some strength you can increase the weight so you can on do 6 reps to failure.

To build muscle you need protein, you should be getting .75 to 1.0 grams of protein per pound of lean body weight/day. (If you weight 110 pounds with 10% bodyfat then your lean body weight is 99 and you should have 74 to 100 grams of proteing per day. Eat at a surplus of 200 to 500 calories per day and lift those weights and you will add muscle (and weight) and you will look great too.