Yeah go back to the Doc and request x-rays like Link suggested. I injured my lower back from doing deads and bent-over barbell rows. I finally went to a chiropractor and found out it was a slipped disc and it also caused me to have sciatica which is no fun at all. The first time i injured my back was during deads and the second time was during bent-over rows. Both times it fell the exact same. Anyway the Doc realigned everything through spinal manipulation, basically twisting me up like a pretzel. I was afraid to go at first because I thought I needed surgery, and I've heard of alot of things can go wrong or make the pain even worse. Going to the chiropractor was the best thing I could have done because it got rid of that nagging back pain that I had for three years. I make sure I keep my back straight with a small arch when exercising now.
Anything worth having is never easy to achieve.