I think back and hip pain may be caused by paint fumes. Both me and my daughter have this issue. Even after the painting is done, the outgassing from the paint causes back and hip pain issues, the time paint is a problem varies by the paint. I totally understand your "Does that sound crazy?" question, because to most people it does sound crazy, I live it. We purchased a different brand of paint that claims NO VOC, and we can actually use it, not problem free, but greatly reduced reactions.
1) use NO VOC paint
2) finish all painting as quickly as possible, repeated exposure to fresh paint sucks for me
3) keep windows open until you cannot notice any odor of paint all after being out of the house for many hours
4) do not sleep in a freshly painted room
I thought I had arthritis in all my joints, mostly gone since 2 weeks into primal, but paint will bring back the back and hip pain within minutes.
Male, 5'11", 49
MaxW 246+ 2004
SW 212 CW 200 GW don't really care
Goal 12+ pullups per set, current 10