noglider 

I can't offer much help, but I'm suffering from something similar.

21 years ago, I had crippling sciatica. The pain centered in the sciatic notch, which is the fold between the leg and the tush, in the back of the leg. It was caused by a pinched sciatic nerve. The pinching was at L5-S1. Since this is nerve pain, the pain can be experienced far away from the site where the cause is. I couldn't walk or stand for more than 10 minutes total throughout the day.

I had surgery to correct this and have been in great shape since then.

But now I'm having a problem with painful numbness in my feet after I cycle a few miles. I went to a neurologist who confirmed that I have a pinch at the same site. I occasionally get pain in my sciatic notch when I drive.

No one really knows the solution, except that my next steps are to experiment with positioning and exercises that strengthen and loosen my hamstrings. I suspect that sitting more upright will help, so I'm doing experiments with handlebars. Yesterday, I went out riding with my wife who is very slow. I took my most upright bike, and the painful numbness was barely noticeable. I'm not going to rush any conclusions.

I'm also experimenting with cleat position. The LBS manager said people are doing weird things lately and getting good results, for example moving their cleats way back so they're pedaling on their arches. I tried that for a few weeks and just gave it up. It was annoying, and it didn't seem to help or hurt. I'm going to try the opposite and pedaling almost with my toes.