i had the same thing happen to me low coolent light would come on but yet no puddles in the driveway till one day i noticed the temp going up and down and the heater blowing cold air like you said. One day coming out of the store i found a puddle under the car put it up on the lift and it looked like the wheep hole in the water pump leaking, we and got a new delco WP and stated tearing it down to find that damn elbo broke. Made me feel kinda good to finaly find out what the problem what for a while i had nightmears of coolent getting into the crankcase!
