Four days after a spontaneous vaginal delivery, a 28-year-old woman woman, G2P2, comes to the physician because of swelling and pain in her right breast. She is actively breastfeeding. Pregnancy and delivery were uncomplicated. Vitals are within normal limits. Physical examination shows a 2-cm tender, mobile, fluctuant mass lateral to the right nipple. There is no warmth or erythema. Which of the following is the most likely diagnosis?
Breast abscess
Breast engorgement
Ductal ectasia
Galactocele
Mastitis
