Look into Calorie cycling. That is what I did for years while in denial to bulk myself up (boy I wish you and I could just trade body shapes right now). Basically it's eating an excess of calories while lifting heavy. You'll gain both fat and muscle during this time. Then, you go on a "cut" cycle where you eat a calorie deficit while still lifting (although less weight for more reps). This causes fat and muscle to be lost but more fat than muscle. So it ultimately becomes a 2 steps forward 1 step back approach, but it lets you stay and pretty much the same weight, build muscle without packing on a lot of fat, and from my experience it keeps your metabolism in a state where you can easily manipulate your weight.