What could be the problem of persistent lower abdominal pain (pubic area)

What could be the problem of persistent lower abdominal pain (pubic area), frequent urination especially when temperature is low? Cystoscopy done 3 times, several scans done, urethra structure x ray done, PSA done, several urine tests done. No abnormal findings been found in any of the above investigations. The urologists says everything is normal and tells you to go home and just drink a lot of water after 2 years of investigating the condition.
However the pain continues. It’s now 11years of this condition.
What could be the possible cause and the treatment?

It’s a musculoskeletal pain originating from symphysis pubis. Focus on that aspect.