I had the same problem. I am only pumping, so I pump a lot each day. I started to get the crack around my nipple also. I know this is silly, but I actually thought "ok if I continue to pump for several more months could my nipple come off". Turns out, my breast shield didn't fit properly. I called Medela and they helped me decide on the right size. I know have two sizes and it works out great b/c if one starts to rub a sore spot I just switch sizes for the next few pumpings.