Hi,

I would definitely agree with Alophysio.... See a doctor who can thoroughly investigate why you are having changes with urination/bowel habits before anything else, even though your Xrays showed nothing abnormal, they don't show soft tissue like nerves, discs, ligaments etc. You may require a more indepth scan (eg Wikipedia reference-linkMRI) or some more detailed xrays (eg side view when you are bending forwards and when you are bending back) as often plain Xrays in standing or lying down don't put you into the posture when you get symptoms. This means if you tend to get symptoms when you're leaning backward, then you should be xrayed in this position to see if there is any "instability" or shift in the normal bone alignment with the postural change.

Either way, make sure you're all clear for anything "sinister" with the soft tissue and nerves, and bones in different postures etc, before launching into an exercise program unchecked.

Good luck.
msk101