Ever change the water pump??
Its a wear & tire item, and it definitely sounds like the water is just not circulating like brettybaby said. Get it checked out ASAP, and dont drive the car. Same thing happened in my old Nissan Sentra.

Water Pump failed --> Crack in Radiator --> Blown Head Gasket. With an aluminum head, these cars warp their heads in the blink of an eye.