I have intense pain in my left leg and need a solution?

This has been going on for quite a long time (months). I first thought it was knee pain and actually had a cortisone injection with no results. Then I had a series of three injections weeks apart and no results. I have been x-rayed and had an MRI. I am 61 and the deterioration is normal for my age and not apparently the cause of the pain. The pain is always triggered when I move from a prone position or a sitting position to a standing one. It takes me several seconds to be able to "work it out" so that I can take a step. I do this by grabbing a door or leaning against a wall or whatever is close at hand and putting my weight on the other leg and then gingerly putting weight on the right leg and then I can move pretty well. No pain. Sometimes I do have pain when I am just walking around, but mostly it occurs only when I first stand up. I am at a loss. Someone said it might be neurological caused by the sciatic nerve. I googled that and truthfully that doesn't sound right either. For one, I have no lower bag pain associated with this. I would love to be able to verbalize this condition but find it exceedingly hard to describe. Any help or advice would be greatly appreciated.