Engine overheating

My SUV overheated the other day to where it was smoking and gushed water from the bottom of car. We filled it with water (was empty) and drove it to mechanic. It ran normally on the 3 mile drive. Mechanic and they said that they couldn't find anything wrong with it. And then 3 days later after driving it, it started overheating again. The 2 times this has happened the car was running and I was stopped. Also the AC blows warm air then the temperature dial goes from normal to hot in a matter of seconds. I checked and there is plenty of water in it now. After thinking about it tonight I don't hear the fan blowing like it usually does but you'd think the mechanic would of noticed that but I dunno. Trying to get it looked at again but they are booked the next 2 days. I really need my car so was wondering if y'all could give me some advice because I don't want to ruin my car obviously. I know its hard to try to diagnose without seeing the car, just thought that I could get some direction :-) thank you so much!