What Causes Burning Sensation On The Leg While Driving?

as i sit and drive, right leg seems to slowly begin to burn. i have no weakness. i know this may seem odd, but reaching forward say to retrieve a paper off the dash, it burns worse. and this will seem even more odd, once it starts this burning feeling, its almost as if its blood pressure related, say perhaps, if i am singing to myself and sing louder , odd i know, but it will twinge or burn more. this isnt 24 hours a day. more like it begins 1/3 of the way into my work day. i am 46 235 lbs.