If your breasts are sore and you have flu-like symptoms, fever, chills, a hard or red area of the breast, or red streaks on your breast, you may have an infection in your milk ducts called mastitis. If you have any of these symptoms, call your doctor. If he or she finds that you have mastitis, the infection can be easily treated with antibiotics.
You may also have a yeast (or thrush) infection of your breast. It's important that you call your doctor if you have any of these symptoms:
Babies with oral thrush may have cracked skin in the corners of the mouth, and whitish or yellowish patches on the lips, tongue, or inside the cheeks.
Sore breasts with a lump also may be a sign of a plugged milk duct, in which a particular duct gets clogged. To help unclog the duct and ease your pain:
Women who have inverted nipples (that turn inward rather than protrude out) or flat nipples (that don't become erect as they should when your baby is nursing) also may have trouble breastfeeding and may experience frequent nipple pain. If either is the case, talk to your doctor or a lactation consultation about ways to make nursing easier and reduce any pain.