Is it time to change food in my food trial?

Hey folks,
I've been feeding Toby NB green pea/duck for a little over two months. He still showed signs of allergies and we've had to get two steroid shots in that time period.

My dilema is that the allergies could be from the food he's on (vet said cats allergic to chicken will sometimes react to duck, cats allergic to beef will sometimes react to vennison), or if it's an environmental allergy... OR he's somehow been sneaking some food (with the kittens and my brother/sister-in-law's cat eating in the house it is a real possibility).

At this point, I think these are my options:
1. Keep him on his current diet for a while longer and hope.
2. Switch him to Cal. Natural herring / sweet potato (which I already have)
3. Switch him to SD z/d rabbit (which is crazy expensive..$49 for a 10lb bag)

So which option do you think I should go with? I'm leaning towards 2, as I already have the food and *hopefully* if he's reacting to NB pea/duck he wouldn't react to the herring/sweet potato...or he'd still show signs and is probably reacting to an environmental allergy.

Any advice / opinions are greatly appreciated.

Art

I would keep him on NB for a while longer. You said yourself that it's possible he's been eating non-NB food.

(I'm doing the same thing with my cat Matilda. She's been on NB since Feb. 15th)

Give it another monthe with the NB.. ONLY issues I see ... if a cat has a chicken allergy it is a HIGH likelyhood duck is also a probelm