tbh, although im a proper carnivore, you dont need meat to gain, most of my protein in a day comes from eggs and whey and milk. About 20% comes from meat, some days more, but would be easy not to.
My bet is your exercise program is at fault here. You probably train too much, for too long, or with the wrong rep ranges. Where you get your protein from doesnt matter, it just matters that you GET protein!
As others have said, dont get a weight gainer, add complex carbs like fine oats into a plain whey shake, have the whey in half or even full fat milk if needed.