ac problem on 2006 Ford F-250 Super Duty

So my ac quit blowing cold air. I checked the pressure and it was very low so I charged it back up. The ac blew cold air for a day or two then it went back to blowing warm air. What's the deal?

Maybe a leak in the system and freon charge is low again??
I got some stuff that is supposed to stop the leak, I will try that and hopefully it works