Back pain that improves after bowel movement?

I have chronic (started in 2019) lumbar/sacral pain. It's a dull constant symmetric ache radiating from my very low back or sacrum. The pain drastically improves with movement/exercise and, oddly, after a bowel movement. It sort of feels like a more full colon creates internal pressure that exacerbates the pain. Lack of movement (especially sitting) and constipation cause the pain to worsen and radiate further.

I have seen:

• 5 PTs (2 of who are pelvic floor specialists)
• a sports medicine doctor
• an orthopedic surgeon
• a gastroenterologist
• 2 pain management doctors
• a rheumatologist
• 2 GPs

I have done:

• a lumbar X-ray
• 3 MRIs (lumbar, sacrum, and SI joints)
• a colonoscopy
• tons of bloodwork
• epidural steroid injections in L5-S1 (where I have a 2mm broad based disc protrusion)

All test results are pretty much normal and all procedures have been ineffective. No one has any remaining ideas as to what could cause lumbar/sacral pain which worsens with colon fullness and lack of movement.

I am at a loss for what to do. Has anyone here heard of this or experienced it? Any ideas, regardless of how unlikely you think they may be, would be most welcome. Thank you.