1999 Pontiac Grand Am Engine overheats, Losing Coolant and

Engine Cooling problem
1999 Pontiac Grand Am 6 cyl Automatic 145000 miles

Hello. My car keeps overheating and for some reason coolant keeps coming out of the coolant resevoir. The heater also blows cool air eventhough the temperature gauge reads over 200 degrees. I've noticed that when the heater does blow hot air, even though it's only for a brief moment, the temperature goes down, but then rises again as it blows cool air again. I've flushed the cooling system a couple of months ago after I replaced the head gaskets and the intake manifold gaskets and switched to the regular green coolant instead of using dex-cool. I flushed the heater core a few days ago hoping it would fix the problem that I have with the heater but it's still the same. I've also checked the two heater core hoses after running the engine for a while and noticed that one of the hoses is hot while the other one, eventhough it's not cool, is not even close to being as hot as the other one. The fans also do work as I took them out and connected power to them directly and they turn on when the temperature gets to about 215. What could be causing this? I'm getting tired of adding coolant every couple of days only to have it come back out.