nipple sensitivity is normal in the beginning. 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 relieve normal sensitive nipples.
Sometimes this occurs, because your baby wants to use you as a teether. Use any teething remedies you find work the best (for example teething tablets) and unlatch your baby when biting occurs.
Some babies have sucking problems that are due to oral problems like a cleft lip.
Also let your baby know that you are unhappy if bitten! When your baby stops sucking, unlatch your baby with your fingers by putting your finger between the corner of your baby's mouth and your breast, before he/she gets a chance to bite.