I was wondering if your back will adjust after a period of time. Perhaps you are doing new twisting and turning that can really throw it out of wack.
Certainly do not have your back issues, however, I do get spasms in my lower back, seems that mine are triggered by stress, a couple of times I could not stand straight, I went from 5'8" to 5'3" in a flash of pain. Muscle relaxers and my mindset has reduced the
frequency.
Have you spoken to your doctor about this? Perhaps there are some other type of shoes that would help, a back support of some kind?
I do not know, however, I would explore all my options B/4 I give up.
Sorry that you are struggling with this pain.