Feeding problems

[Brittany26]

I have an almost 10 yr/old garter snake and he has always been an avid feeder, unless in hibernation. He only eats frozen pinkies, up until 5-6 weeks ago when I introduced night crawlers into his diet. About 3-4 weeks ago is when he refused to eat the pinkies and night crawlers. I was worried about his health so I bought him 5 rosy reds (I know they're bad but he use to eat these for the first couple years of his life and the store had no Guppies). He ate all 5 of them so I figured he was back to normal, until today when I tried feeding him a pinky which he wouldn't eat. I looked in his cage and I have seen little to no poop, other than a small grey spot of poop. Here is a picture of his cage and the grey poop.