All dogs are different in their needs. Some do great on Fromm, as you know some don't. I have had great success with Orijen and Earthborn, those are the only brands of dry food that I will buy. I can tell you that I tried feeding the Merrick Pork flavor to my guys (for the same reasons you listed... price and availability) and now for the first time in his life Otis has the most awful tear stains.
If Claritin, Benedryl or Zyrtec don't help you can try Allegra. That is why I'm currently giving Otis and Tankers for their allergies, it's working great. For instant itch relief you can steep a tea bag in water and use the bag like a cotton ball, rubbing it all over his itchy spots.
Feeding these guys is a lot of trial and error. You just have to be patient and work through the rough spots