Hi and WELCOME!!!
Personally, I would change his food to a better quality food - and change slowly. This food is definitely *not* agreeing w/ his little body, and his body is trying to tell you that. Royal Canin has quite a few allergens in it also, so I'd avoid those. I too would suggest adding some canned food to the diet - both for superior meat quality and added moisture. Brands I like are: Natures Variety Instinct, Wellness, Canidae.