Lower back pain hard to describe.. possible sports injury

I know lower back pain is fairly common: I've had it too on occasion but this new type of pain is perplexing me. I was playing squash about 3 months ago and noticed afterwards I had a sore lower right back pain, almost a hip pain. As long as I stood up straight it was fine. If I tilted my pelvis back and forth I could here a sort of clicking noise and I felt the pain.
The best way to describe it would be to compare it to the feeling you get when you "need" to crack your knuckles. This lower back problem makes me feel like that so I decided to go to a chiropractor. The first session was great. The chiro hit the bullseye with his "adjustment" . Not long after though, the pain returns.
It always seems to come back after silly movements: getting into car, turning over in bed, etc... I've went for at least 15 sessions and am beginning to feel it might be another problem.
I exersice regularly and do ab work (with hopes of helping my back). I love squash but play very defensively because it doesn't take much for the pain to return.
Any ideas?
Thanks

go get checked out for stds