Wondering what causes my left big toe to go numb off and on for the last couple of days?

See your doctor: The usual cause for this to happen is because of a nerve problem, sometimes the lower back has an impingement, sometimes there is pressure on the nerve leading to the big toe. In either event, you need to see your podiatrist or other health professional for evaluation.

Tight shoe: If its confined to the toe on one foot check your shoes. A small nerve runs along the side of the big toe and if compressed can lead to local numbness that may persist even after the pressure is relieved.