Hi lfish, I have a very similar problem, which is pain along the spine, starting from the lower back and extending to the mid-back between the shoulders. It also involves the ribs and restricts breathing/makes breathing uncomfortable. If I do any kind of lifting above my head or hold the camera for too long (as in shooting a wedding for 8 hours) I get longlasting pain in the mid-upper back. Mine is also tender to the touch, particularly in the mid-upper back area.
My question for you is, did you have an accident or injury of some kind to your back? how about to your legs/hips? Have you been evaluated for a leg length discrepancy by a knowledgable practitioner? Have you seen a doctor at all for your condition?
Also, ibuprofen and tylenol don't help too much with the discomfort. Any suggestions?