I read that if you suddenly develop sore nipple
s after weeks or months of successful feeding, it is usually thrush (a kind of yeast infection
). Apparenly, according to "The Nursing Mother's Companion", by Kathleen Huggins, R.N., M.S., a book which you should all get if you don't have it, when you have symptoms
like shiny, reddened, swollen, tender, and cracked nipple
s and it develops after months of feeding successfully it is usually thrush.