I had issues with an obturator a couple of years ago. That's way up in the butt crease, too. I never did figure out what brought it on, but considering the problems I've had since then and the yoga poses that resolved it, my guess is it was coming from a lumbar disc.

Whatever it turns out to be, hope you get it sorted quick. You too, Bike Chick - any chance it's just the mystery aches and pains people get during a taper? I've had those every time...

I did a quick 7.7 with two bridges this morning. I got caught just as the drawbridge came up, which was annoying at first, but while I was waiting I saw a bunch of dolphins and got a call from my mom, all before the bridge came back down.