Hello, my name is Mark and I will try to assist you today.
I don't think you actually have a problem with the headgasket although that could be an effect if you ever forget to top up the coolant in time.
What I would suggest is to check the waterpump seal and also the gasket for the inlet manifold.
These are the two most likely places for a slow coolant leak to occur that are difficult to detect.
For instance, the inlet manifold gasket can leak internally. That allows coolant to escape via the exhaust as steam which you never see.
The waterpump seal can also seep but here the coolant evaporates due to the heat from the engine and again you don't see a physical leak. However you might see crystalisation of the coolant leave marks around the bottom of the pump.
Do you need anything else?