Nipple soreness AGAIN?

Desiree
Anybody know why my nipples could be hurting again? My baby is almost 3 months old, I exclusively breastfeed, and my nipples have started hurting again. Like so badly! Like the first few days after she was born. But nothing has changed. She still eats the same amount, no new schedule, nothing. Any ideas?? 
Edit: I should say they mostly only hurt when my baby is nursing.