Usually not much. Prescription medications are that for a reason, because of increased risks if taken inappropriately or improperly. Diflucan (fluconazole) is relatively safe, but can interact with other medications, causing problems from these. Diflucan (fluconazole) also has a rare association with liver failure, and should only be taken if an indication exists and the rest of your medication and medical history has been evaluated.
Nothing usually. Depends on the amount. At prescription level side effects described by manufacture can happen.