My puppy has diahrrea...?

his 3.5 months old and has all his current shots (corona, parvo..etc)..so, I don't understand the reasons why he would have diahrrea for 2 days now. He does not vomit though, nor looses his appetite. The vet gave him some tablets yesterday so that the diahrrea would stop, and my pup received a second deworming yesterday as well. He went through the "ear crop" surgery yesterday though, so i'm not sure if it has something to do with it. Today I fed him cooked rice, eggs, and chicken; plus, royal canin dry food and Hills Science diet canned food as well. I would really appreciate it if you guys have any advice or recommendations on what to feed him, or do before I can take him to the vet again (in case the diahrrea doesn't stop with the medication).