Car will not stop overheating!?

Here is the problem. My car, a 1997 Dodge Stratus, will overheat at a moments notice. The radiator is losing coolant, fast, with few minor leaks. Its like the car has a bigger leak I just cant find. The thermostat was bad so its been changed. Ive tried 3 different caps with no relief. Ive tried a sealer, that helped momentarily, but only for about an hour. The coolant reservoir stays full, and gets to boiling pretty fast. I add water to the radiator, about a gallon and a half at the time, and it only helps for a little while. Ive tried all I could think of with no solutions.Ive checked the weep hole in the water pump. I do not seem to have water in the oil or vice versa, so Ive ruled out head gasket issues, but the car idles poorly so I may have other issues. Any help would be appreciated!!