Hi Steve.
Sorry to hear about your problems.
I had exactly the same thing happen to me when I was first DXed with AS, I had attended all sorts of Doctors and eventually ended up with an Orthopaedic Consultant and he was treating me for prolapsed discs, however to keep a very long story short he sent me for a MRI scan and on a second visit for X-rays.
After having the X-rays of my lower back and pelvic area taken, the radiologist informed me that I had inflamation of the sacroiliac joint. He then forwarded the X-rays along with his report to my Orthopaedic Consultant who I attended a few weeks later for yet another appointment.
During this appointment the Consultant went over all this different types of treatment I could have for the prolapsed discs, I sat and listened, and told him that I already had all the treatments that he had talked about. He then told me the only option left was surgery and he then went on to tell me the downside and dangers involved.
I interupted him at this point and asked him about the inflamation in the sacroiliac joint to which he replied "THERE IS NONE." I pointed out that the radiologist told me that I had inflamation and it was then that he pulled the X-rays out of their sleeve and out popped the radiologists report along with the pics. (hadn't even bothered to look at the X-rays or read the report)
The Consultant read the report, looked at me and said. "You see all that stuff I told you about your discs, forget it, this is much more serious".
SUCCESS DIAGNOSED AT LONG LAST.

Steve I know exactly what you went through in the past and what Diane is going through at the moment, I think 95% of medicine is GUESS WORK and the remaining 5% is blatantly obvious injuries etc.
So give Diane my best wishes and I hope everything works out in the near future.
Good luck
Ken