I think if you are having problems gaining, a good step would be to up your protein. Guys like doggcrapp recommend sky high amounts, and they are having pretty damn good rate of success. Like try 2xbodyweight. They also hit the protein shakes at 80grams a pop.
i take in my post workout shake with koolaid 100 grams\72 grams of protein isolate in one shake.
If you not hitting ur goal with food etiher eat more, or just add more whey cause whey is cheap. I hit 72 gram of protein per shake usually and drink 2 daily, sometimes a moring shake also, but honestly food is always better. I just make sure i get to 2x bodyweight and see the strenght go up.
If your one of those kids that can eat anything and not gain wieght. Then start eating more 5-6 times a day. Add the protien that was already mentioned and you should see some gains. If it starts to seems sloppy wieght just clean up your diet.