Pain/cramps at 38 weeks coinciding with baby movement?

I am currently 38 weeks pregnant and for the last few weeks I have been experiencing what feels like cramping or stretching pain in my uterus when baby is really active. She always moves but when she really gets to wriggling, its quite sharp and painful down there and nowhere else. I have a high tolerance for pain and this just kinda catches me off guard and is really uncomfortable for the few seconds that it lasts. I tried to talk to my doc about it but, frustratingly, she didn't listen or give me a real answer. Is this normal or should I be worried?