Wait it out; it just takes time for your nipples to get accustomed to nursing. In the meantime, using pure lanolin and/or other natural nipple creams should help.
The nipples may become sore or inflamed for many reasons. Some women experience nipple problems while breastfeeding. Some cancers of the breast affect.
While breastfeeding shouldn't cause pain, tell that to a mother with cracked, bleeding or painful nipples. This condition is likely caused from.