Leak of coolant

I have Chevrolet Cavalier 1997. In enero this had leak of coolant and the thermostat took off to him and the changed the cover of package, but same continue the problem. After, one changed hoses to him, but continue...and after the radiator changed to him, but continue... the mechanic said to me that the radiator badly was made and that the cells badly were placed.
For months four the acr was well and today again leak coolant.....
I don´t know that to do?