He probably has an upset stomach...
I found a really good vet and he told me that dogs are so over weight nowadays. We are killing them with love with all the treats we feed them. Dogs only eat every 4-5 days in the wild, they can go that long without food. And when a dog or even a person eats the same thing daily and then gets something else all of a sudden, they can get sick. You said hes over weight so most likely thats straining his body in every way, in a very bad way. Give him 2 cups of food a day or less and get his weight down...even get the weight down as far as a little skinney then bring him back up. When you put his food down he eats what he wants then walks away, this means hes had his fill...put the rest of the food he didnt eat back in the bag for the day. repeat daily. A dog going without food for a few days is normal and owners shouldnt be alarmed when they do this.