Started smoking a white thick smoke

My vehicle started smoking a white thick smoke that by the smell I'm assuming was coolant. When I would drive my heat gauge would start to climb so I would pull over before it could get too hot so I couldn't drive at all. I of course checked my oil and coolant and both were where they needed to be. I had the radiator checked thinking my radiator must have been cracked and that's where I'm leaking from but there weren't any leaks. So I had the thermostat replaced knowing that by now it has to be stuck and for about an hour it had repaired my problem until the heat started to climb again. What could possibly be wrong with my car? I'm now thinking of having my water pump and head gasket checked but is there something that is being overlooked. Recent History on my car: About a month ago my cars heater would only work if my car was going 40 mph or faster but when slow or stopped would blow cold air. Around that same time my car would start to make this squeaky noise like as if a belt were loose, I have checked the belts and everything seems to be in place. My engine is a 6 cylinder 3.7L.