My ball python won't eat.

[alisha]

My ball python is 2 1/2 years old, it has been almost a month since he has eaten. He usually ate every 7 to 10 days. I dangle the rats in front of his face, he shows no interest and backs away. I have set the rat down in his cage for 20 minutes and he refuses it. I haven't changed the temperature of his cage, he's not shedding, he is very active at night, and he hasn't lost any weight. Recently I switched brands BUT he ate the new brand 2 times with no hesitation. I'm just looking for answers, should I be worried? Is there anything I can do?