1996, Monte Carlo, 117,000 3.1 liters-low coolant light on

I keep getting engine coolant light on. I don't have overheating hapening, at least not yet. I have had a new radiator, water pump, sensor, thermostat, serpentine belt and something else I can't remember what, put in and spent 2500 dollars and still the engine coolant light comes on. I changed the anti freeze at the advice of my oil change mechanic and presently don't use dex cool. Bad idea? HELP