I don't want this to sound like a horror story, but if I knew then what I know now, I might have saved myself several years of excruciating pain, strained relationships with my family, depression, and a very promising career that is quickly going down the drain.
If 1 round of P/T doesn't work, get an MRI ASAP. And, review the report YOURSELF. I recently discovered that an MRI my doctors called "normal" that was done 3 years ago actually showed a small bulge in the L4-5 disc. A little research on the 'net will tell you the size of the bulge and the amount of pain you experience has no corrollation. Large herniations may cause no pain, while small bulges may be excruciating. I previously asked, TWICE, if a provocative discography would be beneficial as a diagnostic tool, but my surgeon said it wasn't necessary. Now that I've changed surgeons, the first thing done was the discography, which revealed a badly torn L4-5 disc. After 4 years, it's pretty obvious this won't heal on it's own, so now I'm scheduled for disc removal and fusion, as I'm not a good candidate for the newer prosthetic disc procedure.
I've not only endured daily pain, but so many procedures, excruciating trigger point injections, surgery, P/T, osteopathic and chiropractic manipulations, countless dollars spent and suffering that could largely have been avoided had I had a doctor smart enough to run the correct diagnostic tests. Damaged discs can be a source of pain, even without any compression of adjacent nerve roots. Only a provocative discography will diagnose this.
I had, supposedly, the best doctors in my area, plus got a second opinion from unrelated surgeons, and still didn't get the appropriate treatment. Seek out the BEST spine specialists you can find, and travel if you must. Do some research online and search these boards for recommendations. I've heard great things about the Cleveland Clinic and the Texas Back Institute, though I'm sure there are many others. I wish you the best of luck. PM me and I can give you some links for a quick education.