Sudden Change in Cycle and Period Pain.

Hi Doctor, For the last two menstrual cycles, I've been experiencing sudden, extremely severe period pain along with diarrhea on the first day of my period. The pain becomes so intense that  painkillers like Meftal-Spas don't help more they worsen the pain, and I've needed  injections for relief. My menstrual flow has also changed. One cycle was unusually heavy, while the last cycle was abnormally short. I recently had a pelvic ultrasound, and it was reported as normal. I'm concerned about what could be causing this. Could this still be related to PCOS. I also started taking ACOD 4 g sachets about two months ago for insulin resistance. Is it possible that this medication has affected my menstrual cycle. I've stopped taking it for now. What could be the possible cause of these sudden changes, and what  treatment would you recommend