If you're not gaining weight its a calorie problem not a quality of food problem. Ideally you should get the bulk of your calories from unprocessed whole foods but changing what you eat isn't going to put you in a caloric surplus, more calories is going to do that.
I know it's hard to face it but it's as simple as eating more, try it and see what happens. add 500 calories to your current macros and if you're maintaining you should gain a pound a week.