1998 Pontiac Grand Am Air in the coolant system

Replaced the radiator, water pump, thermostat, and heater core and when I try to bleed the air out it seems to keep getting more air in it. When I try to drive it the temp will start to go up while cold air is coming out of the vents but then it will start to drop and I will have hot air from my heater again for just a minute then its cold again. Will the intake manifold gasket or head gasket cause this.