Thanks guys. Well the pet store that I got her from was really good about keeping the sexes separate. Sundae wasn't a feeder, and I got her at a different store than Peaches and Squeak. They did have fancy boys at this store but only a few, and they each had their own cage. The only way she could have gotten pregnant is if she climbed into the male's cage, or he into hers. Its possible because they often left the cage doors open half-way, but I doubt it.
Peaches was the one I was worried about when I got her because she was in a tank with boys. But she was so young (though old enough to get pregnant) and I took a chance. I did ask them "Could she be pregnant?" And they were like, "I don't know this is the first time we've kept fancy rats."
At the time, I didn't know how easily rats got pregnant. Anyway, hopefully neither of them are.
Sundae is the one thats getting fat. I doubt its a tumor at such a young age and she is pretty round all over. Hopefully she's just blowing up because she gets fed well now!
LilSouthPaw, I'll take some pics for you and post them. Mike couldn't believe how fat her belly is getting either.
Hmmm, I'm not sure how long I've had her for. I got her in Dec. though.