Feed him something larger, STAT. As other posters have mentioned, a yearling ball python is usually more than large enough for larger prey items. Weights help, as do pictures, but if you can't get us those at the very least offer adult mice at the next feeding. I'd even go for 2 mice with the next meal, if your snake will take it. Go larger until you are offering a prey item at least as big around as the snake, if not slightly larger.

-Jen