What Causes Sharp Left-sided Hip Pain Radiating Towards The Knee?

lets try, i have hip pain on the left side(about center left of the buttock) which radiates down to just above my knee(its fine most of the when laying down) when i stand it will start hurting within a few minutes to the point(severe) where i have to sit down when standing it makes no difference if i m putting pressure on it or not (as long as im standing up) also when i cough there is a stinging numbness on the middle front side of my left thigh about 2 1/2 inch dia. i have had no injuries---this pain started shortly after changing a light bulb in which i had to stretch real high to reach it (i m 6 1)on my tippy toes after which i sat down about five later i felt a quick sharp pain in my hip joint(by quick i mean about 2-3 seconds)then every thing was normal about a an hour or so later is when the pain started--if there is a pinched nerve in my back causing this how do i un-pinch it what do you think is causing this problem?