Not gaining any more weight...?

I have been working out for 4 months. Went from 120 to 142. My muscles and weight have plateaued since then. Not sure what else to do. I am still taking 3 protein shakes including Casein, doing Creatine cycle and alternating my workout days between upper and lower body. Not sure what to do to increase my weight and muscles further. Been the same for over a month now.