My Husband Been On Bendrayl For 20 Years And We

My husband been on bendrayl for 20 years and we went the doctor yesterday or day before n the doctor got him off it n wants him to try a new allergy medicine I had to go get him from work today because he was nauseous bad. The doctor also put him on antibiotics and steroids he is having nose surgery next Wednesday we don't know what is causing this is it withdrawal or what?