I am sorry you are having such a rough time, Tabby. I know how distressing that is. It is like one wrong move and bam! Back to square one. One thing I try to tell myself when I have a setback is that I have felt better before and I will get there again. I'll be interested in seeing what your CRS says.
Val, I wish they could tell you more specifically what they are wanting an MRI for and what they hope to see. I know when I got one years ago when this whole butt pain started they were looking for compressions or a hematoma. Maybe they are looking for something like that?