Why does my dog have gas all of a sudden?

Doggie flatulence is typically attributed to diet. If you've made a change in diet recently, this could be the reason. Dogs can be sensitive to the amount of fiber in their diet and if that's changed or isn't the right amount for the currently dietary needs (age, activity level, etc.), it can cause gas. Maybe give your vet a call to discuss the amount of fiber that's in your dog's current diet and what percentage they think you should shoot for to resolve.