Given the time of year and the age of the animal, I doubt she is pregnant. It is probably worms or some sort of gastrointestinal problem.
And honestly, avoid wasting your money on x-rays or bloodwork to check for pregnancy. You will need to have her spayed eventually anyways, and if the vet suspects a pregnancy over something else (worms, etc) then just get her spayed.
I work in a spay/neuter clinic. I have seen both cats and dogs being spayed while pregnant. It is not our favourite thing to do, but when just down the hall animals are being euthanized because there are too many, you really can't help it.
It is rarely anymore complicated. For dogs it is more serious, but as long as you have a skilled veterinarian there isn't too much more of a risk.
My cat is smarter than your honor student.
Stop Dog Fighting ~ Neuter Mike Vick!
~ RIP Timmy ~ May 2009 - November 6th 2009