Squeaking and not hiding often

my corn snake is about a year old, he has been making a sneezing and or squeaking sound for a while. I was concerned so i took him to a vet to check if it was possibly a Respiratory infection. My corn snake was prescribed antibiotics as a preventative measure but the Veterinarian said my snake did not have an RI but the antibiotics would be good for him just as a preventative measure. It has been month's and I have taken him to the vet twice but he has been diagnosed as healthy and my vet suggested it might be the humidity so i have changed my substrate to aspen/Reptibark and have a humidifier in my room. Recently he has been out a lot laying in the open during the morning and during the afternoon. This is unusual because he is in one of two of his hides most of the time. I am concerned he might be stressed , I do not handle him very often two times a week most of the time and its only for a period of 15 minutes. On a previous note he is still making that sound even though i have done everything I was told to do by the vet.Does anyone know whats going on with him or have had anything similar happen?