What Causes Chronic Back Pain?

I have been having back pain for months, it has gotten increasingly worse and even severe at times. I have had X-rays that show nothing more than some degeneration disc, thoracic scoliosis, and a little bone spur. The Ortho referred me to a rheumatologist. Are there blood tests that my primary doctor can run to eliminate diseases that might mimic each other, or cause my symptoms? I m getting really concerned we are missing something.