Question
Approximately three weeks ago, I was playing some softball and while running to catch a ball, I felt a subtle pain in my lower left back. I played flag football a couple of days later. within a week, I couldn't walk without tremendous pain in my lower left back trailing down to my left buttocks. I went to the doctor and he told me I merely sprained my back and would be fine in a couple of weeks. It gets better at times and then worse but the pain is there constantly. I have started to doing yoga and pilates and it feels better immediately after but then goes back to hurting again. The doctor said that because the pain wasn't below the knees, it was only a sprain and nothing more.   I love to be outside -- triathlons, etc. -- and will do anything except surgery (really scared of surgery). Please help me.

Answer
It sounds as if you have a combination of things happening:  Sprain/strain in the sacroiliac joint, and a spasm in the Iliopsoas muscles.  Doing the Pilates stretches these muscles temporarily, and eases the pain.  As far as pain not being below the knee as a guideline...throw that out.
Your best bet is to find a good chiropractor.  They will asses you, x ray, therapies as needed, and a rehab program to get you back to normal