Back problems are difficult at best to even comment on. Even GPs have a tough time nailing down a back problem (even thought they won't tell you that!). You have already made the right move by going to a sports med guy/gal. Either that or a chiropractor, or back specialist.
Typically GPs get very little training in dealing with back problems. Sure they know how the back works but they suck at sifting through issues of pain and movement to determine where the problem is and what it's cause is.
IMHO for anyone on this board to give you advice on your back problem would be irresponsible considering the serious long-term damage that it could cause.
Back problem are very serious in the sense that they don't just "get better" or "go away" without intense srutiny, and a long road to recovery.
If you're lucky it may just be a small muscular issue that can heal quickly. If you're not it could be an issue with the vertabrae, or connective tissue, discs, etc. and then your looking at feeling that injury well into your old age.
Can you tell I'm speaking from experience??
Further, if you don't feel that the med prof. you're seeing is accurately diagnosing what your problem is - GO TO SOMEONE ELSE. It took me years to find a professional that a. paid attention to what/where/why/when my pain was there b. took the time to do X-rays, tests, etc. c. actually THINK about how to go about fixing what they deemed the problem.
Good luck with that!!!