2001 Pontiac Montana coolant system over heats

summer ran the van with water and winter is here, it over heated while driving, added coolant to the system (all filled up) when sitting the temp gauge will go up and then back to narmal warming up temp some heat will come out then then go back to cold, we did fill it up with coolant and a new thermal, still the same, last i started it a bunch of bubbles shoot into the reserve tank some say head gasket some say water pump! there is no bubbles seen on the oil dipstick, there is no fluid pouring out of the headgasket, i dont know