Run back to Oreillys and get a 'cooling system pressure test kit' from their loan-a-tool program. (call first and make the 'parts man' put their hands on it before driving back).
It's sounds like you're losing water somewhere. If it's burping air, the car won't pull it from the overflow bottle until cools off.
It's sounds like you're losing water somewhere. If it's burping air, the car won't pull it from the overflow bottle until cools off.