Coolant finishes really quick

Hi guys, I'm noticing the coolant is finishing really quickly! Any ideas why? (I'm running the original carb)

Finishing?

Finishing as I  fill up the tank with water and coolant, then in 2/3 weeks it's empty….wasnt like this before

you have a leak or its overheating and boiling up

I can't see a leak anywhere, so it must be overheating…..any ideas what to do if its overheating? I don't see any smoke coming out…..

In my experience;

check drain hole under water pump, wp seal can go
replace expansion tank cap, they can fail
check rad for tell-tale stains of antifreeze leaking
same of interior heater matrix, are carpets wet under dash?
check all jubilee clips and hoses for any loose, aged cracks, splits etc.
check exhaust for white steam if head gasket on its way out, do hoses get rock hard when engine run up to temp?

Thank you....the carpet on the passenger and driver is wet.........

It could be the heater matrix is leaking