It was about 35 degrees this morning coming from work. I noticed that my temp gauge would warm up close to normal, but as I was cruising it went down alittle. Then as I turned on the heat the air came out hot at first and then started cooling off. The temp gauge dropped below the C. SO I turn the heat off and the car heats back up. So I turn the heat back on cause by now its freezing in the car again. Same thing happens. Any idea what this could be? Why is it over cooling when I turn the heat on?

Its was alot colder the other morning and I had no problem with my heat.