Back issues are tricky. Obviously at this point he doesn't have a disc issue or something easy to find. There are lots of small things with your spine though that can be VERY hard to diagnose. I have spinal stenosis, and it took around a year for them to finally find it because it's so subtle. "Taking the shot/pill and getting out there" doesn't work at first, and the surgery has a two year recovery period (it's the same fusion surgery Peyton Manning went through in football last year). Took me several months to learn how to manage it properly. Meanwhile my brother has had a back problem that continues to elude diagnosis for two years.
Back injuries are nasty and literally make your whole body hurt-it's not the same as an elbow or a wrist or a knee where it can be "gutted out" in the same way. Once it's diagnosed he'll have a much better understanding of what to do. Best of luck to him, he's a personal favorite of mine and a great energy player.