Why would i all of a sudden develop an allergy to diflucan (fluconazole)? never had allergies before

Cause unknown: We do not understand completely why someone would develop an allergy to a medication, but it does happen. It is very important that once you develop an allergy to a medication that you avoid it in the future. This is because repeated exposures to an allergen tend to cause worse symptoms with repeated exposures.

Chance: An allergy develops as the result of your gene and environmental interaction. The trigger is usually unknown although viral infection is often suspected to be the facilitator. The more frequently you encounter a drug , the more likely you will develop an allergy to it analogous to the more miles you drive , the more likely you will have an accident.