Check Your oil. If it is milky, that is bad. Also check all your hoses for cracks and tight clamps. Run the car until hot and shut down. Look underneath for leaks. It could be the radiator.
No milky oil. No visible leaks underneath my car. Radiator looks a little funky. Green alongside. Plus the cap doesn’t seem to fit tight enough.
Exactly how much coolant are you losing? Its gotta be going somewhere. Hopefully not out of the tailpipe! Start the car up cold and check the upper hose. See if the cooling system is pressurizing right away