I wonder if he is allergic to chicken -- it is the meat that dogs are most likely to be allergic to. There are a lot of good food choices - ones that are better than Royal Canin. You might find this website helpful
The Dog Food Project - How does your Dog Food Brand compare?
You might want to try a good food with a fish base good - Wellness has one, I'm trying to think who else.
This is another informative site that lists the ingredients of almost every food out there - I would recommend a 4 or 5 star food for your yorkie.
Dog Food Analysis - Reviews of kibble
So glad the bumps & redness have gone away. I hope that Gavin gets feeling better real soon