If you're having serious lower back problems, you should probably see a doctor. Doing stretches or workouts without know the problem can make life worse. Also, be forceful and ask for an MRI. IMO, it's the only real way they see what's going on.
A few years ago, I hurt my back playing tennis. I had a doctor send me to PT without an MRI. The night after the PT was the worst night of my life. After a catscan (sp?) and then finally an MRI, a completely different course of action (or inaction) was prescribed. Luckily, I'm able to play tennis today.
Basically, you need to see if it's a nerve problem or a muscular problem. If pain/numbness goes down to your butt, into your legs and feet you may have a nerve problem.
In any case, see your doctor!