Q: Coolant seems to disappear

If this "just started", it may be that there was trapped air in the system, since you did the water pump replacement, and so all you are doing is providing make up coolant at the moment. But, if the coolant level continues to fall in the coming days, and you have to keep adding coolant, clearly that would be an indication of a leak. If the leak is not visible externally, it could be leaking at the head gasket or at a crossover passageway through the manifold. A static pressure test (cold engine) would help as if the leak is external that test would help identify the location and mark the area needing repair. If pressure won’t hold on a static pressure test and there is no evidence of any external leak(s) that means there is an internal leak which will necessitate partial engine disassembly to diagnose and repair. I would recommend you request a cooling system leak diagnostic to be sure that the leak is not external (external, other than from head gasket area) and thus potentially repairable without major disassembly.