2006 Chevy Silverado 2500HD Duramax Coolant leak

Every 3-4 days my low coolant light comes on and there's not a visible coolant leak although you can smell it after its ran for awhile probably burning off. All pressure gauges in the truck have read fine and my oil level hasn't changed or show any water or coolant mixed in it. I've read where it could be a water pump or head gaskets. The water pump isn't making any crazy sounds although I guess it could be leaking slightly on the bottom side and burning off the engine ( I hope). What is probably the case? (Hopefully not head gaskets).