I highly recommend you read over this very helpful subject in the YT Library:
http://www.yorkietalk.com/forums/bre...-answered.html
I'm not sure if your vet is experienced w/small breeds but you should've waited a little longer to have the xrays taken. @ this stage, an experienced vet can palpate her abdomen & they can tell if the dog is pregnant or not. Please do your research, your pup is now pregnant (maybe?) & needs you more than ever, her life is literally in your hands...along w/her pups. Best of luck w/whelping!