You have to eat more and you have seriously push yourself in the gym. You should barely be able to finish your sets and they should be taxing you to the point of serious strain, but while you can still maintain form and be able to execute 8-12 form-perfect reps. 3 to 4 sets.

I eat ≈3 lbs of red meat a day and I’ve gained 12 lbs of muscle, have visible abs and have gotten markedly stronger in the past year.