Sounds like a blown head gasket or head issues in general.
Usually indicates coolant getting into one or more cylinders.
It can be using coolant even without overheating. Once it's at running temp things expand and can temporarily stop the source of the leak. Pressure check the cooling system and coolant levels as a starting point. Look for coolant in the oil. Pull the oil filler cap, look at the bottom of the cap, and the dipstick. Water and oil don't mix so you'll see the coffee-mate appearance. Then it's onto a engine compression check.