I had two like that and they had pasty butt...as soon as I got it all cleaned off it took them about 1/2 day and they were right back at it again. Make sure their butts are nice and clean...if they are not then you have to run warm (not hot) water over their bottom (trying not to get them too wet) until the poop is loosened, wipe with paper towel while the water runs over it and it will loosen right up and fall off. After you have it all cleaned up take a q tip and rub some olive oil on their butts around the vent area. This will keep it from happening again. Mine haven't got it again but I was sure to add olive oil every evening before they went to sleep. GOOD LUCK hope it feels better real soon!