Sorrry about that CJ-sleepness, I am one of those who wants to know the ins and outs so I can deal more easily with a problem.
It did help me to know what I was up against and other peoples experience.
I did have all the NHS investigations and physio on NHS and private treatment plus home exercises.
Nothing seem to work and I had it for a few years and then suddenly it went and has not come back, to be replaced by Sacroiliac Joint Dysfunction caused by climbing steep sand dunes near Southport.
I went through all the investigations and treatments again including MRI, this lasted a few years, it finally resolved itself earlier last year with the help of cold laser light therapy, now I am pain free.
I am sure the body eventually heals itself but it can take time.