I guess I'm the contrarian one here, but honestly, adding potatoes to most of my meals has not done anything except make me leaner. I eat potatoes sometimes with every meal. And sometimes I have a dessert that has agave syrup in it (oh the horror) and sometimes I have an appetizer before dinner that is dates with cheese stuffed in them, or a pre-breakfast of a half a banana with almond butter. Fat/carb combos that ought to make me a whale, right?
I think you should just eat more. Or drink more wine and eat more chocolate. That always puts weight on me.
Female, 5'3", 50, Max squat: 202.5lbs. Max deadlift: 225 x 3.