Car is getting warmer than usual overheated once, RADIATOR?

-My 97 Saturn overheated last Friday, had it looked at by staff at Autozone, still had anti-freeze in it so came to the conclusion it was the Thermostat. Drove it fine Sunday, stayed at about a little over 1/4 on the temp reading. Parked it outside Walmart, did some shopping for about an hour, came back and there was a puddle of water/antifreeze. Drove it back home ok. My dad looked at it Monday and Turns out my car didnt have a thermostat! He put that in Monday. Tuesday drove the car on the freeway for about 15 min Temp almost at half. Parked the car, and another puddle.

Popped the hood and there always seems to be water/antifreeze on my reservoir water tank. I just put in a new one about 2-3 months ago because my last one was cracked. The mechanic also changed the sensor for the fan because I guess it wasnt turning on and was overheating (this was about 3 months ago overheated at drive thru smoked this time however there is absolutely no smoke)

What might be the issue here? Bad radiator?

Also, theres a nasty like burning smell coming from the engine people tell me its normal but I feel it smells stronger than other cars.

I HAVE NOTICED THE CAR STARTS GETTING WARMER WHEN IDLING OR LOW SPEEDS.

Also, is it safe to turn on my AC? I live in AZ and it just gets too hot here!

THANKS IN ADVANCE!Flush your radiator out, or take it out and get it checked. And the auxilary fan at the front of the car make sure its operating when it should. If the car is hot you should hear it runninga puddle under the car tells me the water pump might be leaking or a leak someplace else. if the radiator was leaking it would leak sitting still. you could have a heater hose leaking down on the manifold.