What Causes Severe Pain In The Legs Upon Standing?

I had mri and went to dr eubanks he referred me to doctor harms my appointment is not until may12 I need to see someone now in my area that takes medicad.m I have disc of mri the pain is bad and I can only stand for afew mins before I have to set down my left leg gets stuck with pain if I am not holding on to something I would probably fall