I've dealt with chronic back pain for years, and physical therapy has changed my life. But I had to have a certain period of time with pain free movement before I could progress.

I also had lots of signs and symptoms that things were wrong before it got really, really bad (I herniated a disc). Knowing how to understand when your body is not in alignment / moving right, and how to correct it, is what the GPs advice is really about. A lot of chronic back pain is due to muscular imbalances; too weak, too tight, too loose, not firing right. Exercises and body work can be done to help correct these things, to ease pain and return functionality.