Exploding water - 2001 Grand Am GT

I'm hoping that someone out there can help me. My 2001 Grand Am GT is acting up. It was running just fine and I even took on a road trip from the Bay Area to Sacramento with no problems. Then a few days after I get back, I'm driving home and someone driving next to me tells me my water is leaking and I look at the temp. Gauge and sure enough it's overheating. I make it home and just let it sit there for a few days since I wasn't able to look at it. Then I go ahead and put water in it to see if I can see where the leak is coming from. I don't see any leak except for the drops that I missed when I was pouring it. I wait a couple more days and then go back to it. Finish filling it up with water to see if there is a leak and nothing. I turn on the car and still no leak and the water level is not dropping. I drive it around a bit and then check the water level to see if it's gone down. Still nothing. So I drive it around some more and then when I stop at the store, and park, I hear the water boiling and then water spills out everywhere from that drainage hose at the resovior tank (I don't know the technical word for it). So I take it back home and when I park it, I hear the boiling again and more water out of that same hose. It's like it's backed up or something. Maybe it's clogged and I need to flush the radiator? Any suggestions?