I just went through the same thing, it was very eina, I was advised by the ladies on the site here to try to not anticipate it and pull her off breast till next feed, I was also tensing up and anticipating it, my dd also got a kick and giggles out of the fact that I said OUCH, so I think she did it maybe to get moms reaction, after a few days I relaxed and now she doesnt do it anymore, you can also keep your pinky finger ready and slip it into her mouth when lo clamps down - I found this helped alot. She is also teething and has been for about 2 months aswell, good luck to you.