Chevrolet cavalier overheating?

Chevrolet cavalier 2002 is overheting. It first showed the sign for low coolant ( which is a squarish tank with waves-lines on top of the tank and an arrow is in the middle pointing down at the waves). i added some coolant and drove less than ten miles and still the car overheated and was low on coolant again. i managed to take the car home. After the car was sitting for a while i added some coolant and checked for any leakes and found none. i then started the car and let it run for a while with the AC off. the car started overheating at about 195degrees, and to my surprise the fan didnt start. The car has one fan and if i turn on the AC the fan works. (I should mention that the car overheats even when AC is on too) The fan fuse and relay is okay. OOHH before this problem started i noticed some thick jelly like stuff in the coolant. I use Dex Coolant. What am i missing. Any help is appreciated and thanks in advance.