Take your car to a good indy for a professional diagnoses
Also a second independent diagnoses is always a good plan.
No point in just guessing what this issue is.
What ever the issue I will have all the parts in stock to fix so a good saving to be had there.
If the head gasket is indeed leaking the coolant can only go three ways.
(1) Into the sump
(2) Out the exhaust to atmosphere
(3) Out the overflow on the expansion tank to atmosphere
If you have a crack then the coolant can also go into the radiator.
However we are getting way ahead of ourselves here as it may be something very simple and cheap to fix.
You say that you have only had the car a few weeks, do you have a warranty or was it a private transaction?
Alex.