Coolant leak, reservoir is empty but it never overheated?

This could be a leak in the water pump or radiator, but to be sure we need to do a pressure test and use a flashlight to see where the leak is coming from. Keep in mind the water pump will only leak when the engine is running. Start with the engine cold and remove the radiator cap, you can rent a pressure tester for free or cheap from an auto parts store.

Here are two guides that should help us:

https://www.2carpros.com/articles/car-is-leaking-coolant

and

https://www.2carpros.com/articles/radiator-pressure-test

Please run down these guides and report back.