Hi there, I know that what I've been feeling lately is similar to what you describe. I don't get the sharp pain, however. I know from my latest x-rays that my right SI is starting to fuse and I have a lumber vertebrae that is growing what I can only call spurs (I cannot remember the correct name). This stiff, burny, overall ache is a sign to me that my disease is progressing.
I sure wish you could get in for x-rays and find out what's going on. This is not something to mess with if you have any kind of fracture.
Hugs,
