What Causes Muscle Stiffness And Weakness In The Legs?

Im a 25 yr old male experiancing muscle stiffness and weakness in legs. My feet and legs are always cold as ice. I have to keep a heating pad on them all the time. Ive had a lot of test done as far as bloodwork, ct scans on brain and thyroid, heart test, etc. Ive seen a lot of doctors and have no answers. Ive been told i might have MS.