I agree with Henry and the insulator. In this period of energy conservation, everyone wants tight houses. Unfortunately, that doesn't work for all climatic situations in our country. Some people have gone the other way and now prefer some of the older houses that "breathe" a little bit.
For your problem, not hiding the windows behind curtains may help the air and temperature exchange at the window. Adding humidifiers and dehumidifiers to keep your air constantly in adjustment with outside humidity will help but is expensive. One expert I read on this problem said to open a window or two for a number of hours every day to allow fresh air and the humidity to equalize although this would increase your heating bill some. I tend to agree that this may be the best way to handle it.
Another idea would be to add an outside air intake for the combustion air on a forced air furnace which I think is a good idea which may help a little. Good luck.