T.D.
It sounds like a plugged duct which is common and not as serious as mastitis. It can turn into mastitis though so treating it just like you have been is perfect. Do you wear an underwire bra? If so you need to make sure that there is no breast tissue being compressed by the underwire. Also, you can take a lecithin supplement to help prevent the fatty part of your milk from sticking in your milk ducts and causing the blockage.