Are you BF a toddler? If so treat both of you, if your bf a new born...have some one take a look to figure out what it is. If it is a sore it could be HSV-1 which needs immiadiate attention. When ds was 1y/o, he bit me and i got the same looking thing on the base of my nipple. I put antibiotic ointment on it for a few days and when he latched on i made sure his mouth was wide open. Good Luck