I just had my oil changed. A couple of days later, my van is leaking coolant like crazy. I can completely fill it and it is empty within hours.
It sounds like there is a large coolant leak, especially if the system is loosing a considerable amount of coolant. The cooling system will need to be inspected for the source of the leak. Many times the source of the leak, especially if the coolant is boiling away would be a white residue at the leak point would be visible. If the leak point is not easily visible then a coolant pressure test may be necessary to locate the leaking component. You may want to enlist the help of a mechanic, such as one from YourMechanic, who will have the training and equipment to determine the leak source of the cooling system and will be able to repair, test, fill and bleed the cooling system.