Nipples are hard?

The other day, after an afternoon of naked crawling, we noticed a hard knot in Maddy's nipple. Her right nipple was enlarged and red and hard as a rock. The next morning, it seemed okay so we didn't worry. This afternoon, I noticed it was hard as a rock again. Geez. What gives? So between the crazy fevers again, swollen neck glands and this, we're taking her to the doctor in the morning.