I have the same problem, but my pain is on the right side. When I sit down the pain radiates from my upper buttock to my ankle. My leg has a tingling and a little bit of numbness while I'm sitting. I'm about 75 lbs overweight so I thought it may have something to do with the weight. What concerns me is the pain is now radiating from my lower back/upper buttock area to the side and front of my abdomin. I go to the Gyn on Thursday, because I first thought the pain right side of the abdomen was female related. I'm really confused and concerned now.
have you ever heard of a siatic nerve. alot of times if you have had children or overweight this can be a problem because the weight of the baby or being overweight puts pressure on the nerve which causes severe pain. i developed it when i was pregnant and also my mom has it too. i think there is surgery for it if it is really bad. talk to your dr.
good luck
Sounds like you have either bulging or herniated disc in the lower back, get an MRI,that would definately verify it.