Welcome back, Poppa John! I used to get lower back/sacral area pain when I stood for very long, but it's gotten better. It takes probably 15-20 minutes of standing before my back starts hurting now, and my knees (mainly the one that hasn't had surgery yet) start hurting earlier than my back. The swaying/weight-shifting helps my knees, but like you, it doesn't really help my back.
Do you think some core-strengthening exercises might help? Strengthening your abdominal and back muscles would help give your spine some support when you stand. You might consider asking for a PT referral.
Ginny - 58 year old female
Dx with USpA in March 2013; changed to AS in July 2015
Iritis and Scleritis, both currently in remission
unicompartmental knee replacements: right-June 2014, left-Aug 2018
MTX, Humira, Cyclobenzaprine, plus Celebrex as needed
Supplements: Folic Acid, Vitamin A, Vitamin D, Calcium, Fish Oil, Culturelle probiotic, Melatonin (as needed)