Definately talk to your doctor. Also, I was told by my chiropractor that ice is the best thing for back pain, ten minutes on half an hour off. If you use heat make sure it's moist heat not dry. I had hashimotos before my thyroidectomy, and had constant back pain, when my chiro took xrays I was shocked to see that one of my vertebre in that part of my back was turned slightly, also my neck is not curved like it should be and my head is on crooked (this explains alot)ha ha. Are you currently seeing anyone like a chiro? The one I go to doesn't do the manual adjusting which is popping and cracking. I go in and he tests my weak points, by pushing down and pulling out on my arms, then he has me lay on my stomach while he positions foam blocks under my hips or wherever i need it andI lay on them for a little bit. Then he uses a tool, I guess it is a percussion type instrument that taps the pressure points. The best part of the whole treatment is then end, when I get to lay on the spinalater. It's a massage table. You may want to try this method instead of pain medication. It is safe even for babies. In fact his daughter and grandaughter both had their first adjustments before they were 1 week old. I have had significantly less pain even after just two weeks, three times a week.
Don't know about the drug interaction you are having, but maybe this will help with your pain.