There are 3 kinds of sore nipples:
Most nipples have led a sheltered life before breastfeeding. So for the first few days, there will likely be some tenderness - like when you get a new pair of shoes perhaps.
As a baby begins to breastfeed, it is normal that there are a few seconds of ouchy pain as the baby draws your nipple into the right position. This should go away after 10 or 20 seconds as you settle into the feeding. (Even this diminishes over time.)
Then there is pain that lasts all through the feeding, lasts in between feedings, seems to be getting worse instead of better. You may see raw spots or cracks on your nipple and there may be some blood mixed in with your milk. This pain is not normal nipple discomfort. This kind of pain is fixable and you need to get help asap.
Sore nipples, especially those that match this last description, are most often caused by the baby latching onto the nipple improperly. It only takes a time or two to turn healthy nipples into painful, raw, red or blistered nipples. Also, a baby who is latched onto the nipple improperly is not receiving your colostrum or full milk supply as he is not massaging the ducts behind the nipple. He will be frustrated and perhaps more aggressive on your nipples, making matters worse.
Make sure your baby is latched deeply onto the nipple. A large part of your areola should be in the baby's mouth. Bring the baby to the breast chin first rather than straight on, the same way you jut your chin forward and open wide when biting into a super deluxe hamburger.
Examine how your baby is latched on (the lips should be flared out, not tucked in). If you aren't sure, take your baby off and relatch. Tickle his lower lip with your nipple and wait for him to open his mouth wide (as wide as when he is crying or yawning). Don't let him gum his way onto your nipple with a half opened mouth. Patience pays!
Try breastfeeding when your baby is just waking or you are beginning to notice his feeding cues: chewing on his fist, turning his head in a rooting motion, making sucking movement with his mouth and tongue. Crying is a late feeding cue saying he is frantically hungry. Start nursing sooner and he will be more patient and his suck will start out more gently.
Begin each feeding nursing your baby on the least tender side. His suck is strongest when he is most hungry at the beginning of the feeding.
Position your baby differently on the nipple so the same sore area is not continually irritated. Switch to the football or side-lying position.
Change bra pads when wet and do not wear bra pads that have a layer of plastic in them. The plastic traps moisture against your nipple and the effect is like chapped lips.
Spread a thin layer of ultra-pure lanolin (Medela Tender Care Lanolin or Lansinoh™) over your nipple after air drying. You don't have to wash it off before you next feed your baby. Other lanolins may contain pesticides, alcohol and detergents which may further irritate a raw nipple. You can also safely use a hydrogel dressing between feedings. This is a superhydrated medium designed to speed healing of damaged tissue and is very soothing.
Your nipples have their own lubricating glands. Avoid using soap when you bathe which may further irritate and dry your nipples.
Some moms find it helpful to apply wet, warm, tea bags for 15-20 minutes directly over your nipples after a feeding. Then air dry your nipples. When dry, squeeze a drop of your colostrum or breast milk onto your nipple and rub it in (it's very healing and soothing).
Shells (not shields) worn over a sore nipple keep clothing from rubbing and allow for further air drying. Use the wide ring in the shell.
Take a mild pain reliever such as Tylenol™ or Ibuprofen one half hour before nursing.
If you get to the point that it is just too painful to breastfeed, pump the sore side with a good cycling pump, and feed your baby the expressed milk with a cup, syringe or bottle. Do this for 24 hours. This will give your nipples a chance to heal. Ease back into breastfeeding (nurse one time, pump one time) and make sure the cause of the problem is corrected so it doesn't happen all over again.
Meet with a lactation consultant to help assess what is causing the soreness. She will help you position your baby and teach your baby so the soreness does not return.