You need a bone scan to see if screws correctly in place and an MRI for soft tissue issues. I also had a CT w/contrast. They each showed part but not all of the problem. My pain sounRAB so much like yours. radiating to my hips, butt, now it has moved to my legs being nurab and painful just as before the first fusion. My problems are moving fast at this point. My saving grace was getting all of the radiology reports and reading them prior to going in, take them to your GP if you don't understand. I truthfully do not think my surgeon would have done anything if I had not started referencing reports.
Good Luck.