1992 Pontiac Grand Prix water in res

wehn we start the car in the morning hear in michigan temps around 20 degres. the car will heat up. heat will work. start to drive about 5-10 minn. the car over heats and the antifreez backs up into the overflow contaner. we let car cool down let pressure off by opening radiator cap water returns into system. the car runs fine after this process. please help!!!!!
have changed thermostat twice.
new pump
new radiator
replaced top hose

thanks
johnspag