One thing to remember is a side effect isn't necessarily an allergy. A true allergic reaction will land you in the hospital, but a mild allergy or a side effect, while bothersome, won't necessarily hurt you. There are anti-histamine meds other than benadryl that can help with the itchies, that's actually a VERY common side effect for a lot of narcotics. I'm just worried that if you go in this surgery saying your allergic to pretty much every standard after-surgery med and want something real strong, they will think your a drug seeker and won't give you anything for pain, and you definitely don't want that. So maybe ask for a different anti-histamine to go with whatever post-op pain meds they give you. Good luck to you.