I had the same and it did turn out to be thrush in my case and it cleared up with prescription nipple cream for me and some nystatin for my LO. If you don't want to go the prescription route or aren't 100% sure it's thrush, you can apply sterilized water and baking soda (1 c water, 1 T soda) to your nipples after every feed. You can also apply it to your LOs cheeks and tongue with a Q-tip. I do this anytime I get strange pains or any discomfort when BFing because I figure if it is thrush, I'll nip it in the bud before it gets bad, and if it's not, it can't hurt baby or me. I also took ibuprofen (and sometimes naproxen) for the pain - I was told it's safe when BFing.