Do the overdrive light suppose to be on while driving

With the switch in the off position it will stay on, (light) If the light is flashing then you have a problem...

Agreed. Light on means "Overdrive Off" and your 4-speed automatic will be fine driving around town with the light on. But on the freeway, at speeds at or above 50 mph so it will not shift in to 4th gear. So bush button on shifter (not the button to take it out of Park, the smaller button below that) to have Overdrive - meaning 4th gear. Light should go off. In it doesn't go off, there is a problem.. and joemom is also correct that if it flashes then it really does need attention from a transmission shop asap