Hi it has a leak and if it has a leak it is not getting up to a working temperature. so it must be costing more to run as it is doing less miles per gallon. so where is it leaking from this may be a variety of places some exremely expensive and some cheap so take to the car dealer for a check.
Check you engine oil, then check you exhaust for white smoke or a sweet smell. Lastly get a compression test, to check your engine's cylinders heath. Losing coolant is really bad, most likely your head gasket is failing.
run the engine at high temp at idle and look for signs of water leakage around the engine itself.,ie water-pump , thermostat housing cylinder head gasket , radiator. expansion tank.
If you see white smoke your losing coolant either you have blown gasket or leaky gasket
i keep filling it up but it disappears but not when its sitting only when i drive it
