James,
Even though you say you have the humidifier turned "off", it may still be putting some moisture into the house. To make sure it is off completely, shut off the water supply to it. In addition, you could also shut off the air supply to it from the hot air plennum. I assume you have forced air heat.
Other things to do are to run the exhaust fans when you are showering and cooking.
Good Luck!
Dodgeman