pregnancy

Question
How can I tell if my dog is pregnant.  She has been throwing up and is showing signs of having swollen tits.  I don't thing another dog has gotten to her but I can't be sure.

Answer
If it has been more than a month since the middle of her season, a vet can tell by palpitation or X-Rays.  Although false pregnancies are common, vomiting from them isn't.  Perhaps another reason to visit the vet.
  
I think it is irresponsible to not either learn enough about female dogs that you don't have to ask such basic questions, or get them spayed.  It requires extensive preparation to produce quality puppies.  Those unwilling to do so should have their dogs spay/neutered at 6 months.