If he had a bunch of worms, he may have an upset tummy or be constipated from trying to get rid of them all. If he doesn't make a good poo today and still won't eat, I would get him back to the vet for a recheck. It does sound like his little bum is bothering him, whether it is painful or maybe even itchy. If you don't see anything external, I recommend seeing the vet sooner rather than later. Poor baby isn't having a good week.
