I have a 2000 Grand Prix and i am having problems with The coolant/possible leak?

im gonna be honest I hadn't put coolant for a while and it overheated the other day when I was driving home it splashed all over everything.. so I went out and bought some coolant and put it and it seemed like there was a hole it was leaking out then I stopped and it stopped as well so I took it as maybe I overfilled it. I got in the car and started driving and the "low coolant" light had turned on again even though I just put some I didn't feel it al the way to the top but I did feel 50-70% of it! through the "engine coolant cap" and the other little coolant cap where other cars usually take their water., I checked it again today and it was the same so I put a little more to fill it up and it was leaking again! a lot this time! so I stopped filling it and it stopped leaking ...I then tok it for a drive and on my drive way were little spots where it was leaking...while I drove it no coolant light turned on and no smoking and the thermometer was perfect. I got home lifted the hood and it was splattered all over the top of the engine and everywhere else...what could it be? I amr eally worried this is my only car.