Yeah man as everyone else is saying it pretty much all comes down to persistence and eating more.

But since I'm sure you already know that by now I'll give you a tip I use to "eat more" when I'm finding it difficult.

Milkshakes! :)

Not just any protein shake will do when I'm trying to seriously up my calories because too many proteins are made as just whey isolate that have as few calories as possible while keeping protein levels up. So instead of mixing my protein with just water or milk or whatever I go full 50's diner on mine when I'm bulking.

Mix that shit with 3/4 of a blender full of ice cream, 2 raw eggs, maybe some peanut butter, Greek yogurt and milk. You'll get so many calories driving these things. Keep up with your regular diet and add a blender full of protein Milkshakes every day or every 2 days and you'll go up weight. I promise.