A head gasket leak can start small and grow. Mine did this over the course of about a year. A decent shop can run a quick test to detect combustion gasses in the coolant.

A free trick than can tell you a lot is to go for a ride and let the engine thoroughly warm up. Leave it idling and go open the hood. Release coolant pressure by halfway unscrewing the radiator cap. Does the engine change note in how it runs?

The engine does not have to run badly with a blown head gasket. They can run just fine. In fact, sometimes they can run better due to having the chamber(s) cleaned up.