I recently had my ac checked out by a technician because my ac did not work, it would run but no cool air would come out. The technician advised me that I needed freon so he did indeed put freon and hours later I had nice and cold ac. But only for it to go back to running warm again 2days later. Do you know what could have caused this?

Sounds like a leak,, needs to be located and repaired

Based on the problems I had last summer, it could be a freon(whatever coolant) leak, or unfortunately could be the reversing valve which makes the compressor unit about worthless.
I think the only solution is to have a reputable tech look at it. Hard to diagnose on here (even by an expert, which I am NOT) without you testing stuff and reporting back to them.