My Puggle has major flatulence problems. Nothing seems to help.?

I have a puggle that is about 1 and a half years old. He has had this problem for months now. I have tried switching his food. I have used Royal Canin, Innova, and now Taste of the Wild. None of those helped. I also use a slow feed bowl, and I have bought digestive enzymes and gas relievers for him, and that helps a little sometimes, but it is still terrible. It is very smelly, and embarring when I have guests over. What else can I do? I was thinking of getting some yogurt to put on his food, but it seems like I need to find the root of the problem. Also maybe I need to keep changing foods? I don't know. Someone please help.