1995 Buick Century HeadGasket leak

For the last 4 months for every 800 miles or so I have to add about 2 quarts of oil to the car. The oil is leaking into the watercooling system into the coolant reservoir. The car overheats a little on occasions. But the weird thing is that the water level stays the same I don't lose any water and there seems to be no signs of water in the oil. Is there any other possibilities other than headgasket leak? Also there is no kind os smoke comming out of the tailpipe