Are you feeding him in a bowl, or a way, so that he eats more slowly? We use a combination of things for this: first, the bowls are elevated and they're the ones like this. I also have a hollow, rubber globe/ball that has a hole in it i fill with food, along with a kong, in which I fill with food. It amuses her (and us) to watch her eat. And she is extremely food-motivated so she'd eat all her food in 10 seconds otherwise. The other thing you may think about is if there's any activity that you all do, or do with him, which coincides with the one month periodic problem. Eg, we have 'steak night' once a month and I was giving her the T-bone, which she threw up the next night.