The prednisolone that was prescribed for Pepper is not actually an anti-histamine (which is normally used for allergies). If you believe it is allergies maybe you should ask/(demand) from the vet an actual anti-histamine. I know that there have been a couple of threads here that talked about using Allerga or Zyrtec for cats (and it seems to work). Clariten should be available over-the-counter (i.e. in the drug store) in about a month, so you might want to try something like that. If you are going to ask for an anti-histamine make sure that you avoid anything with a decongestant (e.g. Clariten D), it could make Pepper ABSOLUTELY wired for hours and hours.

I hope that everything goes okay for him