car started runing hot now heater quit blowing warm air 1998 lumina

How low did the coolant, get? Maybe you have air in the system? As far as the heater, are the heater hoses, hot? The blower motor works, correct? You may need to check coolant flow through the heater core. I can't rule out problem with temp actuator? How hot does the engine get in degrees F? The radiator fan works, correct?

The question is why did you loose the coolant to begin with. When you refilled the cooling system you must not have purged the air out of the system. Look for leaks.