If you are experiencing coolant loss and there are no obvious signs around the unit, have a butchers at the engine undertray to see if it looks wet, and from there have a look round the bottom of the cambelt cover. Using some tracer dye helps a lot.
The water pump can fail and it's a good idea to change it when doing the cambelt, saves time stripping that side of the block down. Inlet manifold gasket can also be at fault for coolant leaks.
Not intending to depress you any further but unless you have the paperwork for it don't necessarily believe it's had a new cylinder head gasket change, or that it's been done correctly using the MLS version and the stronger oil rail underneath. Oh, and the heads sometimes can go porous, although a new core one ain't too dear at the mo.