Hmmm...Could you have a plug of milk there? Is it open? Could it be a blister? Do you have any other soreness? Try to nurse on the least sore side first so the strenght of your babies suck is lessened on the sore side. You could try a warm compress. Keep the area clean and dry as possible. You can rub a few drops of breastmilk on it after a feeding to help fight infection. If it doesn't clear up you may want to see an IBCLC or a good doctor.