Ditch the mass gainers and start calorie counting. You also required to count your Total Daily Energy Expenditure (can check from my sig) to know your required amount of calorie intake to achieve your goal.

To make it 'easier' for you:

I have a TDEE (maintenance calorie) of 2500kcal. To aim for bulking, add another 20% which make my Daily Calorie Intake to 3000kcal.

I consume 1 serving of Mass Gainers which give me 1500kcal. I need another 1500kcal to achieve my Daily Calorie Intake. Throughout the day, I only manage to eat another 1000kcal. Total Calorie Consumed for the day is 2500kcal. OOPS, it's the same as my TDEE. I will not gain any weight at all.
Response: I need to eat more.

The same situation above but without Calorie Counting.
Response: This mass gainers doesn't work. Time to head to forum and ask for a better mass gainers.