Coolant/water contamination?

A week ago I was greeted by a white cloud of white smoke (water vapor) when I started my car. This has never happened before. The smoke cleared after a couple of minutes. For the past week every time I start the car the white vapor is always present and clears after a few minutes. Today I started the car i the morning and there was no visible white cloud. I drove the car non stop for 3 hours on a long journey on the highway. I reached the next town and stopped at a traffic light. When I drove off the white cloud appeared and was there for about 10 minutes driving at low speed in town. When I rejoined the highway it cleared. I reached my destination after 20 minutes. When I stopped at the traffic light and drove off the white cloud appeared again. Very thick. There seems to be no evidence of burning oil so it is definitely water vapor. Have I blown my head gasket? Any suggestions and solutions will be appreciated in advance. Thank you