Most women who breastfeed will experience plugged ducts at one time or another. If you have a plugged duct you will probably tenderness and soreness in one part of your breast. It may be red and develop into a hard, painful bump. It is important to treat a plugged duct promptly because untreated; the condition can worsen to mastitis. Mastitis is a painful infection marked by breast soreness, aches, and fever.
Treatment for Plugged Ducts

Mastitis
If your symptoms get worse, and if you start having flu-like symptoms, you may have mastitis. If you suspect mastitis, contact your health care provider as soon as possible. Mastitis is often bacterial and antibiotics are frequently prescribed to treat it. It is important to get mastitis treated quickly so that it does not turn into a bigger infection that would require surgery to remedy. It is also important to take good care of yourself. Get a lot of rest, eat well, and stay hydrated.