have you seen or talked with a chiropractor, spinal specialist, or kinesiologist? They are much more specialized in the working of the spine. I have SI Dysfunction (which does not describe your symptoms) and also had 2 herniated discs (which does describe your symptoms in the beginning), and other spinal issues...so I've worked with spinal dr's a lot. What you describe does sound like it could be a disc possibly going bad. Especially having RA, your discs have an increased risk to herniate. Since it resolves in a few days, it likely has not herniated yet, probably just swelled due to inflammation. I would recommend the X-ray as your rheumatologist suggests. An Xray can not show the disc itself, but it can show if the spacing is off or if your losing space which will indicate if a disc is in trouble. They can go from there to see if it needs treatment or not.