Doctors don't always agree with each other, and sometimes they cannot help as much as a physical therapist can.

In late 2001 my lower back began hurting, especially on bike rides. About a year earlier I had started paddling a rec kayak; I was armpaddling, of course. I wondered if the kayaking had anything to do with the back pain, because I'd been cycling for many years pain-free. One area of my butt under the sit bone also felt "off." Doctor gave me some stretching exercises, saying that my hamstrings were a bit tight. He told me to do more abs strengthening exercises, even though I was already doing 100 crunches every day. I did the exercises and they helped a little. But not enough. The pain continued in spring 2002, so the doctor referred me to a physical therapist. (At this time, I also began fixing my paddling technique, and I switched to a sea kayak that fit me better.) The PT used deepheat massage for the sitbone discomfort, which did eventually go away. He also started me on additional strengthening and stretching exercises to stabilize my spine. After a session or two with some improvement, another PT in the same office examined me and discovered that one of my vertebra sometimes did not line up correctly. It was an intermittent thing. They had me work on strengthening, stretching, and BALANCE using a Swiss ball. If my spine was funky, we would "teach" my ligaments, tendons, and muscles to help keep it aligned.

Upshot of it all was that *several* factors contributed to my back pain:

* Random misalignment of that one vertebra ("you were probably born with it")--this may have contributed to the tight hamstring on one side, among other things
* Poor crunch technique--I had gotten sloppy over time, so I was straining lower back muscles instead of strengthening abs
* One of my cycling shoe cleats had gotten twisted, causing a small misalignment of foot/pedal/crank that probably exacerbated the vertebral misalignment
* The old arm-paddling style probably torqued my lower back, too

The good news is that the pain did go away. I still do my exercises. The only time the pain reappears is when I do something "unbalanced" such as lifting heavy things on one side.

But I didn't post all the above just to gloat. Point is (are) that it'd be worth getting a 2nd opinion, and that there could be several causes of your problem. In my case, I could have blamed the pain on kayaking, but that really wasn't the cause; it just was the straw that broke the camel's back.

Good luck!