The biggest problem is the cabin size. The volume of air is small in comparison to other cars. What is happening is, due to the outside temps dropping, the surface area of the window is cool. The air in the cabin is full of moisture from your breath, perspiration etc. The air is touching the cold window causing it to drop below it's dew point and this is causing the moisture to condense onto the windows.
It will clear eventually if you can get the cabin temp up and keep a high fan rate. The a/c effectively acts as a dehumidifier all year round which removes moisture from outside air coming into the cabin before reheating to heat the cabin.
You will notice if you have air con on and turn off, the car will fog up quickly and smell a bit weird. This is due to the moisture on the air con coil getting carried into the cabin by the hot air once it turns off.
It's all a bit weird if you don't understand air psychrometrics.
Fact is air con could/should be used all year round due to low ambient temps and high saturation of the air.