Hey there, thought I'd chime in on this topic.
Is it your lower back that is in pain? Your kidneys are a lot higher - mid back. If the pain is down low, just above your butt cheeks in the pelvis area, it is probably a condition called Sacroiilitis. Inflammation of the sacroiiliac joint. I was diagnosed with this in 2005. I had a bone scan done to diagnose it.
I notice it flare up when my fibro flares. seems to run together, for me anyway. But the pain is excruciating. I actually feel better if I can keep moving. Sitting or laying for long periods of time makes the pain worse.
I got a prescription for a topical cortisone cream that's 10% cortisone. Very powerful stuff. It works really well. Heat works too. I know what it's like to have back pain. it's awful. Anyway type in sacroiilitis into google and see what comes up. Your rheumy will know what it is too.
The headaches are pretty much par for the course with lupus and fibro. I take extra strength Tylenol. That's about it.
Ginny