Michael,
It's hard to picture that tiny, cute little puppy in the video being overweight,
but I know it happens. One of my friends had a yorkie that was very overweight, and they put it on the diet dog food and started an exercise program and the vet couldn't figure out why he still wasn't losing weight.....turns out my friend was always feeding him yogurt drops (about a can every 2 to 3 days
) and puperoni as treats. When he exercised he got even more treats, so he had actually gained a little weight while on his diet before the vet figured it out. LOL. Maybe if you give him a lot of treats, you can cut back on those as well and that might help. You don't need to feel bad either, you were just spoiling your baby rotten.
It's something we all do. I'm sure in no time you can get him back to a healthy weight.