Laurie, based on the way you describe your pain and the improvement I’ve had since surgery, I’d say if your doc won’t order it, find someone who will.
Since surgery I have had NO sacroiliac pain. Granted, I’ve not done a lot and I’ve been well medicated, but I haven’t even had a hint of it. Find a student of this guy:
http://thesteadmanclinic.com/dr-marc-philippon.asp
When you do have your MRA, ask the doctor to block your hip when he’s in there to inject the contrast. He is going to be using lidocaine to block the tissue for the injection anyway, so it’s not a big deal to block the joint. Not only does it make the test more comfortable (they jam a lot of crap into the joint capsule) it’s diagnostic. If the block makes you feel better at all, that’s pretty indicative of a labral tear.
Something that was interesting about my pain is that manipulating the leg didn’t cause sharp, instant pain. It was sore, but not crazy. But when I walked out of the doctor’s office, I was hobbling with fairly general hip/back/i-don’t-even-know-where-it’s-coming from pain. Turns out that in addition to the tear I had, I also had a swollen, hypertrophic labrum, and it was getting pinched and blistered with movement. Explained a lot about the pain I was having.