I have an old very big female garter and she's being housed with one of her children in a large tank and they have been very very good together. How ever today I noticed that she has an odd new shape near her vent. She is much skinnier right before her vent which makes it look like the section of tail right after the vent is swollen, but I'm not sure if it really is because it could just be that she's skinny right before. She then started squeezing her self through as many tight tubes and holes between things in her enclosure and visibly squeezing near her vent as though she was trying to give birth or make a bowel movement, and then she even began to open her vent and push, it almost looked painful. they were fed about a week ago and they are fed pinky mice. She is very calm as usual and let's me touch her even around the vent area with no protest. What could be wrong?