The discomfort over the incision should have resolved by now. Some people take longer to heal than others, so there isn't necessarily anything wrong, but you should probably have it looked at. Infection could cause it to be persistently uncomfortable. Topical vitamin E can help a scar heal, but doesn't usually address pain (it is more for the aesthetic component).
They used your internal mammary artery (not your mammary gland) to supply blood to your by-pass. I would check with doctor on why area is still tender...