This post will probably annoy you, but its true. You will have to eat more, or to put it another way "eat more than you burn off", stick to that quote and you WILL gain weight, if you want to gain muscle mass, lift heavy and make it 3 sets of 5-8. I had trouble gaining weight untill recently - and yeah im an ectomorph like you, i pretty much had to double what i eat in a day. If Ironfist replies to this post he'll be a great help - he was to me, thanks Ironfist!