Buy a couple of dumbells (30lbs each or so) and do chest flies as often as you can. Those are when you're lying on your back, with your arms extended out, bringing the dumbells up in a half-circle until they meet. Do them slowly and until you're so exhausted that you can't will yourself to lift them one last time. Your bed is a good place to start if you don't have a bench. It's amazing what chest flies will do for your pecs. Six months of that multiple times each week and I guarantee (well, no, I can't) that you'll have muscle there where you currently have fat.