92 Cavalier Radiator/Overheat Problems? Help!

Last night I was tooling around town no problems, top down, breeze in my hair...

Anyway, stopped off at a friends for about an hour, then as I was leaving I noticed my temp gauge was in the orange, and my check gauges light was on. I stopped at the gas station to buy some emergency coolant, but the coolant reservoir would only take about half of the jug. Started the car after about 20 min and drove to the next gas station as my gauge was in the red again. This time I added oil, and went on my merry way only to have the problem repeat. My fluids are topped off, and my car sounds absolutely fine..but the gauge is in the red! I turned around, went back to friends house and stayed...now it is morning and I have NO clue what to do.

SO, radiator cap has the lil red/orange tab on it that I must lift before unscrewing the cap. Do I have to do something special to the cap to make sure that the vacuum is created in the coolant reservoir? I did notice that when I first popped the red/orange tab on the cap, that some air escaped and some fluid came out from under my car...

This may be a super simple problem, but I cannot locate my Chilton manual and am just stumped. Anyone have any ideas for me?

Thanks so much for your help...
~ChiChi

thermostat, VERY simple