Gained weight, but in tummy :/

So I have been trying to gain weight since last six months. I am very skinny and quite weak. I have been trying to eat a lot more than usual but I can't do a lot of weight training because of screwed knees and rotor cuff on the right shoulders. So I have been doing mild activities like Pilates and Yoga. I have gained 10lbs but it seems like everything has gone to my stomach. My tummy is now noticeable even after wearing clothes.

25M 5'7 106lb -> 116lb

I have no clue what to do. I just don't seem to gain any mass at arms or legs or anywhere else.