...cooler or cold....? When I get started again the heat goes back to hot. Is it a vac hose that may have a leak ?

check you antifreeze level, sounds low

the thermostat is bad .. it is hanging open. it needs to close as the engine cools off.to keep the engine at the right operating temperature .By closing the amount of water that passing through the engine is smaller so the water heats up more and the engine heats up as well . When the water heats up the heater get warmer. now when the thermostat hangs open so much water passes through the engine so fast if over cools and thus the heater gets cooler .. replace the thermostat and you fix your problem.