Chevy Cavalier Running HOT

I have a 96 Chevy Cavalier, 133,000 miles. I requently get some dummy lights luminating. Such as the check engine, and now a new one that is like a box with a wavy water line and an arrow pointing down (no idea what it means!) I've had the car hooked up to the code checker thing and they always say that I have a hose lose and that's why my check engine light keeps coming on. And that it will only cause my gas milage to decrease. Which this has not happened. So just about a week and a half ago, I filled the coolant and checked the oil. However, one of my "dummy lights" remained on. The box one will not shut off. So now my car can not idle for any more than about a minute and a half and the temperature gage starts climbing rapidly! And now today I just make it back home before the little temperature needle reaches the RED area and when the car was turned off, it was dripping the coolant that I just had put in not that long ago. However it's not dripping from the radiator or any hose. Any ideas on what could be wrong and about how expensive it's going to be to fix?