Not to parrot others here, but knowing a bit more about your system will help us and you make the improvements you're after and really fine tune any suggestions. You mention you're taking a mass gainer before bed, but what does the rest of the diet look like? What does training look like? Example to make sure you're getting enough nutrients to build the muscle you're after.
That being said, I would recommend Ergonine and Anabeta Elite. Ergonine is a complete performance enhancing product, and it would take the place of your creatine. It contains several other ergogenics PROVEN in humans to cause some form of strength, endurance, or lean mass gain. The main purpose for this is to ensure you're doing everything in your power to ENHANCE your training abilities.
Anabeta Elite is your anabolic here. This is whats going to shuttle more of the nutrients you're eating towards building muscle. Its also going to stimulate your appetite, furthering this effect. When you combine all of this with superior training, you get GROWTH!