If you want to gain mass you need to eat more. That's really all there is to it. I am in the same boat as you right now. Except I am stuck at 175lbs at 6'0''. To give you an idea of what a normal day of eating is for me.. I am eating 6 eggs and lots of bacon every morning. Dinners are usually a pound of meat and a pound of veggies. Lunch is a little under a pound of chicken, half pound of veggies. I also take two scoops of whey on my workout days. Plenty of snacks too to try to get more calories in. I haven't kept track of my calories since getting on this diet back in june, but I think I am eating about 3500-4000 cals a day easy. So like I said, if you want to gain some mass.. start eating!