Snake won't eat.

My ball python hasn't eaten in 2 weeks. The only thing that has changed is food size. 2 weeks ago I moved his rat size from small to medium and he ate it just fine. Then last week I tried to feed him again and he wouldn't eat it, so I wanted till this week and he just smells it and goes back into his hide. He doesn't appear to be losing any weight, but this is my first snake and I am a little concerned he doesn't seem to want to eat. I do use frozen rats if that matters.