Hello, An allergic reaction may occur at any time even years after using any particular drug but the same thing applies to all potential offenders (allergens). Sometimes it s very difficult (if possible) to determine the cause of an allergic reaction. If the biopsy is very suggestive of drug allergy then switching to another drug is advised. Otherwise you can try to eliminate other potential offenders like swimming in the pool (particularly since the symptoms seem to have appeared after you started going to the pool, am I right?). You can also check whether you ve started using other substances for the first time like a new shampoo or fragrance, etc. If you can t identify any other suspects then changing your blood pressure regimen sounds like a good idea. Hope I have answered your query. Let me know if I can assist you further.