How can i gain weight!?

Im 17, 6 foot two and barely 160lbs, i go to the gym often eat quite a bit but my metabolism just breaks everything down and i dont gain muscle mass ive checked everything i dont know what else to do? try a weight gainer? eat some sort of special foods? slow my metabolism somehow? i want to gain weight evenly not just on my belly because my stomach is flat and i have abs but my ribs, arms legs shoulders etc are all pretty skrawny. im sick of it can anyone help?