Pontiac Repair: 99 firebird is overheating., pontiac firebird, radiator cap

Question
I have a 1999 pontiac firebird 3.8L v-6. Its been overheating on my laterly. I changed out the thermostat and ran it for a few hours with the a/c on and it seemed to be doing ok.I noticed the temp gauge going up on me again today so I pulled over and opened the hood and sure enough antifreeze was boiling over the reserve tank. I was using the a/c and could smell antifreeze also. I turned of the a/c  and put the heater on and the temp regulated.  The only other thing I can think that can be causing this it the water pump could be going out or maybe even the fans. Any help or suggestions would be appreciated. I have another car  I can use but this one is alot better on gas than my GT. Thank you.

Answer
1. MAKE SURE THE A/C CONDENSER AND THE RADAITOR ARE FREE FROM BUGS AND DIRT . CLEAN CLEAN TO LET AIR FLOW, CHECK AND MAKE SURE FANS ARE OPERATIONAL AND THAT THEY COME ON AND SHUT OFF, AND WHEN THE A/C IS ON THE FANS SHOULD BE ON OR COME ON MORE RAPIDLY, DOUBLE CHECK THE RADIATOR WHEN COOL TO MAKE SURE THE COOLANT IS FULL,, AS WELL AS THE TANK, CHECK AND SEE IF YOU HAVE A BAD RADIATOR CAP,