Well, the vet said that he didn't have any sort of infections (he checked his poo and all for any sign of parasites, etc.), but to be on the safe side, he gave him some antibiotics. He seemed to think that it could just be this time of year. He did seem to think that Apophis was a little overweight, so I'm going to be doing better care on him and watching his feeding. Being my only adult snake, I hadn't realized that he needed to go longer between eating than my hatchlings and young adults. I'm supposed to watch him and see if the bulges near his vent go down, so I'll keep everyone posted. Thanks for the replies everyone, especially BAH. It is appreciated!