What Causes Pain In Lower Back And Legs While Walking?

Lower back and back of legs hurt when walking, sitting and standing. I tried to walk to relieve but can t walk too long, stretching doesn t work. Doctor just says I need to lose weight, but even bending is painful. I am losing weight, but it still hurts. I know people heavier than me that can squat and bend and walk better. I take advil occasionally, when I have to. I try not to too often. but it only helps a little anyhow. I am so tired of this! any ideas...I was even considering acupuncture???