Help!

I am 10.5 months postpartum and have exclusively breastfed my son, aside from table foods. He’s always been a great nurser. All of a sudden, it is excruciating to nurse, especially my left nipple. Nothing has changed that I know of. The right bothers me too but not nearly as bad. Just the nipple hurts, not my entire breast. It’s not thrush (I had that several times with my son and know what that feels like). I do not think it’s mastitis or a clogged duct as it’s just the nipple. Any ideas???