I saw Sally this morning, she is 99.9% sure that it is a bulging disc at L4-5 or L5-S1 due to the symptoms that I get. And when I do the cobra movement, it improves. Next appt is 4/5, I am to stay off the bike til then, and continue the stretches. She said an MRI would not be a bad idea, just to confirm or rule out disc issues.
As for bike fit, I have had 2 done by the Specialized BG fit system. At this point, it may be helpful to be more upright on my bikes. And I have put mtb racing out of my mind til I am 'fixed'.