Where am I losing heat from my house?
Find an isulation installer that is a certified thermographer. An infrared scan of your home should reveal where the heat loss is occuring. The best time to do this is when the outside temp is lowest and your house is warmest. The problem could be missing or improperly installed insulation. Without a scan you are only quessing what the problem is. Ask about a repeat scan after any repairs to verify the problem has been resolved.