Consider your shoes, more supportive shoes may help on long walks. I over pronate, and when my sneakers are at all worn down, I start to have back pain.
Also, jogging or running would often make things much worse for me.
I overpronate badly and do carefully choose my shoes to support that. But, if I just avoid being on my feet for too long at a stretch I never get back pain.
Also, jogging or running would often make things much worse for me.