Hi Milo,
Without a sonogram or an x ray it is not easy to be sure if a dog is pregnant because dogs can go through a false pregnancy during the third stage of the heat cycle which will show all the same signs of a pregnant dog. In pregnancy you will see weight gain, enlarged teats,possible milk discharge later in pregnancy and some nesting behaviors. However you can also see this in a false pregnancy.
You vet may be able to feel the pups through abdominal palpitations after day 26 or so, but this is not always possible.
I am going to direct you to a site on pregnancy and false pregnancy to better help you.
If she is pregnant usually birth is around the 63rd day and the body temperature may drop to 99 degrees .
pregnancy http://www.petplace.com/dogs/pregnancy-in-dogs/page1.aspx
false pregnancy http://www.petplace.com/dogs/pseudocyesis-false-pregnancy/page1.aspx
dog training consultant
24 years training & behavior,pet first aide, Therapy dog eval., PA Animal Response Team