Did you read my post? First question...Is your needle on your temp gauge atleast 1/4 to 1/2 into the the blue after 5 or 10 min?
If YES and No heat: Look towards your heater core and or baffles in your hot/cold mixture.
If NO (i.e., the needle isn't moving after 5 or 10 min or moving VERY little): Your motor is not heating up fast enough. In this case, try the cardboard...ITS FREE!!!! If this still doesn't work i.e., the needle doesn't come up in 5 or 10 min, replace the thermostat.
Troubleshooting CAN BE very expensive and very frustrating...if you don't do it right. Do the stuff that is FREE first. The next thing is to eliminate questions. Example. If you car wont start, you need to deterime if it is spark or fuel. Pull a plug and if it sparks while you crank the motor, you know the spark is good. You have just eliminated replacing the battery, the coil (if it has one) the distributer, plug wires, plugs...etc.
Back to the first question...Is your temp guage showing that the motor is warming up in 5 to 10 min?