What Causes Severe Backache?

My wife is experiencing severe pain that runs along her spine in the middle of her back. Hurts constantly, but worse when laying down. OTC meds don t help. It s like a severe bruise, but nothing is visible and it is progressively getting worse. More of a dull pain, not sharp. Has brought her to tears. She is going to the chiropractor tomorrow and they will do xrays, but I think it is more than a pulled muscle. More on the boney part of the spine than to the side where I would think it would be if a muscle sprain, plus it s been three weeks and getting worse each day. She does have a little tingling in one toe, so maybe a pinched nerve? I appreciate the help and any suggestions. I m pushing her to get in with her regular doctor.