It's likely your dog could be pregnant. I have to ask though, if you knew your dogs weren't fixed, was there a reason you let them get "stuck"? I mean, mixed breeds can sell (depending on the breed) but if you weren't planning on breeding them, is there a reason why you didn't get them neutered/spayed? Doing so is actually a benefit for the animal. I'd be glad to refer you to some online information for future reference. Just let me know if you are interested.