Oh u can def get endo on your sciatic nerve. Mine is cyclic as well with my period. My past few cycles i feel my sciatic flare up to the point where i can walk

Keep looking for an endo specialist who knows their stuff. I've been fobbed off for years by GPs who told me to "go take a hot shower" or it was just my period or "women's problems" which are supposed to be painful. What a pile of crap :) insanely, before I was diagnosed on weds, I actually climbed the Andes on my period just before Christmas. It was exhausting and I don't know how I did it and I did end up catching pneumonia (our immune system goes down right?) but amazingly that was a rare time when my lower back and sciatica were OK (usually I'm just in bed or have to have a hot bath) which maybe proves constant strengthening and movement helps it. I know we can't all hike for 14 hrs a day but it may be something to do with the extra oxygen going round the body. I'd started training (just hiking) a few months before and I'd been hiking for a couple of days when it hit which may be the key. When I haven't exercised it usually really hurts x

I've seen so many GPs who don't know about endo so I wouldn't take their word for it. I've just been diagnosed with endo on my pelvic wall which explains why I've always needed to push my lower back to relieve pressure when I'm on. To me, the idea that maybe it's pushing or on my sciatic nerve makes total sense. I've read that certain dells of endo can even end up in the lung (just cells) which then also bleed and hurt during periods. Makes total sense it could be on sciatic nerve. Why else would it occur then? I have pain down my legs too x

I'll respond more in the morning (getting late here) but found these very interesting (pdf files from medical journals):

http://www.lmaleidykla.lt/ojs/index.php/actamed...

and

http://www.bjj.boneandjoint.org.uk/content/90-B...

I don't know if an MRI would always show adhesions, but it seems like a very promising way to get an idea if there is something going on.

Just want to clarify I am not someone who hikes up the Andes all the time! I just happened to do it for charity once and as luck would have it my period started. Usually it would have floored me (we were sleeping in a hut with no toilet!) but I'm telling you there's something in this increased oxygen going round the body thing. Also maybe endorphins to release the usual tension? xx