You need to take in lots of calories. You want them to be good calories, lots of protein and carbs, but try not to eat a ton of fat. But you need to take in more calories than you burn in order to gain weight. Keep on with the protein shakes, have a couple a day. When you work out, do short reps with heavy weight. The shitty thing is if you want to gain mass, you're not going to stay cut. You have to put the mass on, and then cut it.