Thanks to all of you for the info/advice. I realize that it's a back problem but I believe that it's brought on by the bike fit. I was concerned that the lower back issue and siatica didn't appear until after the fit. It's a totally new issue on my part. I'm old (56) but in excellent health; 12-13% body fat, low cholesterol, low triglyceride level, blood pressure (128/70), and resting pulse of 50 bpm. I see my doctor tomorrow, Tuesday.