What Causes Severe Pain In The Lower Abdomen On The Left Side?

I get periodic severe lower left intestinal pain. It comes without warning and I have been unable to link it to a fodd or eating or not eating etc. it lasts from 1 hour to 6 hours. Nothing seems to eliminate it, it ends on it’s own. I have chronic constipation, but this happens even when i’ve Had bowel movements earlier the same day. I have had 2 previous colonoscopies and was told that I have a floppy colon, but no other irregular findings. I thought it might be diverticulitis and my doctor prescribed a course of antibiotics but that didn’t seem to help. Ideas??