i always get those when my ds is cutting a painful tooth. i think he rubs his teeth on my nipple when he nurses at night for comfort. i feel it happening, but its not that painful till the next day when it turns into a blister-like thing. ouch! they really hurt. sometimes when this happens i will only nurse him on the non-painful side for a few days, and will pump the side with the blister so i dont get mastitis on top of it.... other times i just try to distract myself while he latches on to the painful side and just nurse as if there werent anything EXCRUCIATING happening over there, lol......they seem to last abot 2-3 days in thier most painful form and then the pai n subsides while they heal for another few days...
SOunds like a 'plugged pore' or, as others have said, a milk blister. They're usually filled with solidified breast milk. I had one and my LC recommended flaming a sewing needle and *GULP* lancing it, followed by gently squeezing the nipple. This huge, long, spagetti-like thing came out and 8 hours later the pain was gone and all was well. Not for the faint of heart tho.
I just saw your posting now....I had one of these for six months. I know exactly what you mean...it looked like an embedded whitehead, it was hard and the area was tender. I finally got rid of it by soaking my nipple in cup of water as hot as I could stand it and then just expressing, expressing, expressing milk through it. After the nipple had been soaked and expressed, the blockage came above the surface and I pulled it out with very clean tweezers. The area healed very quickly after that. I know that picking can cause infection so I'm not recommending picking, just telling you my own desperate experience. I can definitely tell you that soaking the nipple in hot water and expressing milk through it (do this 1 or 2 times a day if you have to) can really help.
Sounds like what I had when my daughter was about 3 months. It was refered to as a Milk Bleb. I used comfrey root to help it heal and it worked overnight. I am a Master Herbalist and learned of this in my studies. It was noticibly better within minutes. Take Comfrey root and boil it in water on the stove for about 20 minutes at a tumble pace. Then take a large piece of flannel (I used a clean folding diaper) and soak it in the liquid, once it is cool enough place it on your breast and hold for a good while. Resoak when nessessary. This will not effect the milk flow or the taste of your nipple with your child. Good Luck. I can remember bitting my lip with intense pain, then doing this, and then not feeling any pain at all.