Rinse your nipple with warm water (no soap). Warm, moist compresses (wet washcloth works well) often bring relief to nipples. Apply lanolin cream on nipple after air drying. Apply enough to thoroughly coat the entire nipple/areola area. Recent studies seem to indicate that using 100% lanolin may hasten the healing process by maintaining the internal moisture of the skin. Avoid other creams and ointments sold for the treatment of sore nipples as these may actually impede healing by preventing air circulation and drying out the skin.
The soreness may also be due to a fungal infection (thrush). You need to show yourself to a doctor for this. Treatment includes the use of Miconazole cream applied to the nipple and areolae 2 to 4 times a day for 7 days and this should be continued for 2 weeks beyond the end of the symptoms.