Why does my dog fart ALL the time?

My dog is farting, not exaggerating, ALL the time. He seriously does not go 5 minutes without farting. And you can't hear him fart, you just suddenly smell it and its awful! It just started 2 days ago, so its not natural of him. We didn't switch his dog food at all, so I don't know what else could be the problem. My dog is medium sized, if that helps. Someone please tell me how to keep him from farting! It's unbearable!