What Causes Severe Pain On The Back Of Thigh Radiating To Ankle?

for about 6 months i have had leg pain in the back of my thigh in my left leg. I thought it was from not working and would take some time to loosen up and become pain free. it has not. it has been getting worse. the pain come and goes but without several excederin in my system i can barely walk and lift my leg. the pain now at times will shoot down from the back of my left thigh to my ankle and stop there and hurt very badly. on occasion it will shoot up from the back of my thigh to the bottom of my buttox. the pain is mainly on the back of the thigh 90 percent of the time but will shoot to these other specific locations at times. i also have started noticing very yellow looking big bruises throughout my body, even my arms, but especially on my bad leg. What could be wrong with me?