This could be due to a disc that is bulging or any number
of things. I think your physio did the
right thing in ordering an
MRI etc so that you'll know for sure. I would in the mean time, however, avoid prolonged standing activities and practice positions where your back is in a more "open" posture, for example, lying on your back with your knees and hips bent and hugging your knees towards your chest. This should take some of the pressure off the nerves in your back.