There are usually 3 things that will cause a car to over heat,
1, Bad radiator (or holes in one of the radiator hoses leading to and from the engine). it you need to keep adding coolant ,
2. A bad water pump that is supposed to move the water between the engine and radiator. if the Radiator is and reservoir are full but the car is still over heating then you probably have a bad water pump.
3. A leak in the head gasket which i letting water into the combustion chamber. Check to see if there are any signs of water bubbles or water marks around the engine block. you will sometimes see steam coming form the engine the engine when its hot. or the coolant turns a thick yellow. number 3 is the worst case as repairing it is costly.
but it sounds like you have air in the cooling system so check the hoses