What Causes Pain From Groin Area Across Thigh To Inside Of Knee?

I am a 65 year old overweight female. I have arthritis in my spine, knees and hips. I try to walk everyday for exercise and used to do 2 miles a day but can only manage 1/2 mile now. I have a lot of pain but the thing I would like help with is the stinging, searing, pain that will shoot down my leg from the groin area across my thigh to the inside of my knee. It is so painful I cry and cannot move until it passes. Sometimes a slight positional alteration will alleviate it, but that only happens about 2% of the time. It is particularly bad when I try to walk up or down a steep incline or ride a bike. Could this be a saphenous nerve impingement? And what can I do about it. I have suffered with it for 4 years now and can't take much more. Thank you