If you are loosing coolant with no apparent leaks, then you may have a blown head gasket. This is very serious and will in time ruin your engine. If you have white exhaust smoke with a sweet smell, that is a good sign of blown gasket. Also bubbles at the radiator with the cap off, is a sign. Have this looked at ASAP.
Your heater core could be leaking, but that would smell like antifreeze. You could have had a windshield replaced by a moron, or you could have had body panels replaced by the same moron. Unfortunately you need to stick your nose in there and see if it smells like antifreeze, coz that's bad news Phil
needs a new heater core
It could be a partially blocked heater core, a faulty heater valve that allows the coolant through the heater core or it could be a faulty water pump.
coolant smell/leakyes more than likely that's your prob. but could be maybe a hose.
It could be that your head gasket is blown.
Could be oil mixing with antifreeze indicating a bad head gasket Are you losing motor oil?
the heater core could be stopped up, or could be low of antifreeze, or the thermostat could be stuck open
if it rear air and heat it could be the line carring the antifreeze tho the back heater core.
It could be that your heater core is blocked or damaged somehow.
Could be the heater. It's likely that most of the hoses to the rad were changed, but maybe a hose to a heater (if you have more than one), or the heater itself.
could be a cracked radiator, bad radiator cap, a busted radiator or heater hose, bad heater core, or a busted fill box!
Passenger side floor? Could be leaking heater core