How long have you been feeding Orijen? When was the switch completed?
It does take some time to get the old stuff out and the new stuff working.
However if it has been a while I would def. consider switching to the fish formula. Could be a reaction to a protien source ( such as chicken) in the regular formula.
Best bet is to find something that is VERY different from what you are feeding ( if you have been feeding it a while) if it is allergies to food, you have to remember that they cant have treats either which contain the possible culprits. ( whether it be corn or chicken)
Have you talked to your vet about Benadryl too in the even it is seasonal?
Courage is being scared to death and saddling up anyways. ~John Wayne