Go rent a chemical combustion gas test kit from your local auto parts store. Basically it's a large syringe that you place into where your coolant pressure cap goes and it is filled about 1/3 of the way with the special blue liquid that turns yellow when combustion gases are detected in the coolant. You will have to purchase the liquid separately. This is the most simple, sure fire way of confirming a head gasket leak into the cooling system, and if you do detect combustion gases in the coolant, then it'll be up to you to decide whether or not you want to take the necessary action to repair it properly. If you don't, then consider other possibilities such as thermostat issues, cooling fan issues, restrictions, air pockets, or even water pump issues as well.