get your blood sugar checked. i'm a retired architect and started experienced burning and cramping in my lower legs while climbing ladders stairs and walking irregular job-sites. went to the m. d. thinking it was old disc injury re-surfacing. nope it was type 2 diabetes which had developed a blockage in an artery in my groin. you're lucky it got both my legs. when you walk your muscles are demanding more blood-flow i. e. oxygen that they can't get so they burn and cramp. after decades with diabetes i've found that long seated positions can exacerbate weakened or diseased vessels (common to diabetes). needless to say i spent many hours doing that at my desk or a drawing board. good luck
what may be the cause of my left calf muscle to burn when i walk. i do sit for hours at work. i have had mri and the mri appeared normal.