As long as the natural supplements come from a reputable source they should be fine, but the JAMA has a recent cautionary article on some of them:
http://jama.ama-assn.org/cgi/content/short/292/23/2868
I started having thoracic problems after doing a yoga stretch/exercise (extension)in summer 2003 after spending months lying down. All my muscles went into extreme spasm, and since thene I have had pain much like yours. Docs vary, blaming cervical and thoracic discs, but I suspect it is an inflammation of fairly calcified / arthritic ligaments. Being able to move around more normally, time, gentle stretching, and power strengthening seem to help--and expecially, lots of time.
Bruce