That seems to be another symptom of ME/CFS .. Ive spoken to several with severe ME over the years (bedriddens) and they all had extremely bad period pain. I dont thou know if its a symptom that the sicker we are the worst it is.. or if its just a common symptom in CFS/ME patients. The ones Ive spoke to before about it.. they apparently were fine with their periods before they got CFS/ME. The kind of extreme period pain we were discussing was the kind which goes right throu the abdomen, radiating throu the back and right down the thighs to the knees. I actually one time went almost completely fainted or may of for a moment while driving (I pulled over the side of the road unable to drive more as it was so bad). I was driving to try to get treatment for it.. as I was crying with it even after taking two different kinds of pain killers together and the hot water bottle wasnt helping either. Amazingly this guy who was a chiropractor on that occassion helped it. He grabbed this large area of my abdomen, inside my pelvis very deeply (it hurt) and pulled and stretched it.. it brought in instant relief which lasted for a few hrs or so. I've tried to replicate what he did but have never been able to grab myself deep like that and pull.