Still not running. The reason, I think, is a case of sciatica: pain along the sciatic nerve, which runs from the lower back all the way down each leg. Typically it manifests only on one side, anywhere along the nerve. In my case, on the left side, around the lower back/hip/buttock.
I’m feeling much better, but not 100%, and I don’t want to take any risks. So until I am 100% I’ll listen to the Mayo Clinic: “For most people, sciatica responds well to self-care measures. These may include use of hot packs or cold packs, stretching, exercise and use of over-the-counter (OTC) medications.” I just hope it doesn’t take 4-8 weeks for it to go away.