So sorry to hear you're having this problem! I feed my dog Addiction, which you may want to try because they use novel proteins like kangeroo/brushtail/eel which your dog may not be allergic to, you can read more at their website - www.addictionfoods.com
. It's supposed to be great for very sensitive dogs. I would also follow the excellent advice given by other posters on how to eliminate possible trigger foods. The friend who introduced Addiction years ago to me has a golden like yours who is allergic to everything
, and as a result he's on the Zen Vegetarian dry food plus a bunch of homecooked. I know vegetarian formulas spark off a whole debate and I really don't want to go there, all I know is that my friend's dog is healthy and beautiful. I myself rotate between homecooked (beef), Addiction salmon bleu and addiction raw dehydrated lamb.
let us know how your dog is!