Are you measuring your temperatures at all? I know there are some people in south east asia who keep ball pythons with little to no extra heat just because of their climate.
Check your temps. Shoot for 90ºF on the hot side and 80ºF on the cool side.
Start tracking the weight of your snake. Aim to feed 10-15% of the snakes body weight every 5-7 days. For a hatchling, one adult mouse is probably fine. Please don't over feed or you might be looking at another regurgitation.
Wait 2 weeks before you feed your snake again. This will give the animal some time to recover. Regurgitation is very stressful on the body and it is necessary to give them some time to recover before offering another meal. You want him to keep the next one down!