Thanks for the replies. I already have heating pads stuck all over me (sweating like crazy as I sit at my desk), but will also try a foam roller. Based on the stiffness (in addition to the pain), I'm guessing that it is an injury around the hamstring/glute area, which come to think of it, was growing a little sore after several hard rides now. I probably put the final nail in the coffin when I trudged up and down the stairs with water jugs after Saturday's ride.

I'm also going to make a Dr. appointment to get the PT ball rolling, just in case this does not go away soon.