I had this happen to me too, and it's usually either the pad material irritating your skin or moisture buildup down there during your period. What worked for me was switching to pads with better breathability, changing them more frequently, and making sure the area stays as dry as possible between changes, so maybe try that first. But since it comes back every cycle and causes you pain, might be good to bring it up with your gynae or PD just to rule out any sensitivity or infection, especially if it doesn't improve with the pad change.