Ball pythons are notorious for going off feed in the winter months. Starting at about their second winter, most BPs will start eating irregularly anytime between November and March. It can be really frustrating and worrysome if you've never been through it before.

Make sure everything is right in the enclosure: temps, humidity, cleanliness, etc. Then make sure your snake is healthy: a trip to the vet for a fecal test and general look-over. If your snake is fine, and your setup is good, it's probably just normal BP behavior.