A couple of quick questions:
1. Is your furnace working? Do you feel exhaust heat when you are outside the vehicle near the exhaust vent? Your furnace may not be igniting and you only hear the fan.
2. Have you checked the heater tubing in the basement? You may have some kinks and blockage. If this is the first time you are using the furnace in cold weather, this might be a problem that wasn't apparent in warm weather.
3. How cold is it outside?
4. Do you have your window shades and night blinds down all the way? Windows are a big heat loss problem in cold weather.
Hope this helps.