It can be treated by varying the babys feeding position and applying heat before feeding. If it happens more than once, further evaluation is needed. Milk stasis is an urgent matter for mothers who wish to breastfeed, as failure to remove milk from the breasts causes milk production to decrease and eventually stop. Mastitis
Mastitis is an inflammation of the breast. It causes local pain (dolor), redness (rubor), swelling (tumor), and warmth (calor). Later stages of mastitis cause symptoms of systemic infection like fever and nausea. It mostly occurs 2–3 weeks after delivery but can happen at any time. Typically results from milk stasis with primary or secondary local, later systemic infection. Infectious organisms include Staphylococcus sp., Streptococcus sp. and E. coli. Continued breastfeeding, plenty of rest and adequate fluid supply is the best treatment for light cases. Overactive let-down
Overactive let-down (OALD) is the forceful ejection of milk from the breast during breastfeeding. The forceful spray of milk can cause the baby to consume too much milk too quickly as well as to swallow air during the period of rapid swallowing following the let-down. Raynauds of the nipple
Nipple pain can be caused by vasospasm of the nipple. In essence, blood does not flow properly to the nipple which causes the nipple to blanch. This can be caused by trauma to the nipple through early breastfeeding or candidal infection of the nipple. The pain is intense during the latch stage and in between breastfeeding sessions there is a throbbing pain when the nipple is blanched.
Breastfeeding difficulties refers to problems that arise from breastfeeding, the feeding of an infant or young child with milk from a womans breasts. Although babies have a sucking reflex that enables them to suck and swallow milk, and human breast milk is usually the best source of nourishment for human infants, there are circumstances under which breastfeeding can be problematic, or even in rare instances, contraindicated. Difficulties can arise both in connection with the act of breastfeeding and with the health of the nursing infant. Breastfeeding problems
While breastfeeding difficulties are not uncommon, putting the baby to the breast as soon as possible after birth helps to avoid many problems. The policy of the American Academy of Pediatrics on breastfeeding instructs to, "delay weighing, measuring, bathing, needle-sticks, and eye prophylaxis until after the first feeding is completed." Many breastfeeding difficulties can be resolved with research based hospital procedures, properly trained nurses and hospital staff, speech pathologists and lactation consultants. Another source of information is the volunteer-based breastfeeding promotion organization, La Leche League. A variety of factors and conditions can interfere with successful breastfeeding:

Ankyloglossia (tongue tie)
Formula feeding
Distractions or interruptions during feeds
Long separations from the mother
Tachypnea (rapid breathing) such as in transient tachypnea of the newborn, surfactant deficiency, respiratory distress syndrome or other infant medical conditions
Presence of an actual physical barrier between mother and infant
Swallowing difficulties such as with prematurity and coordination of sucking, swallowing and breathing, or gastro-intestinal tract abnormalities like tracheo-oesophageal fistula. Pain resulting from surgical procedures like circumcision, blood tests, or vaccinations.