not sure if dog is pregnant

Question
Hi,
I had my german shepehrd bred during her last heat.  i wasn't sure she was pregnant so i took her to our vet for a blood test.  it came back that she wasnt pregnant.  that was last week on what would have been her 46th day.  Last night, i noticed a sac around her nipple and she was acting aggressive towards my other female (shih tuz)this morning.  the gs was under the bed and the shih tzu went under and the gs was growling and making all sorts of weird noises.
could she be pregnant with only 1 puppy and thats why the test came back that she wasnt pregnant?

Answer
Hi Carrie

The could be a number of reasons that your pregnancy test came back negative, one being she isn't, the other is human error.

That being said, what other signs is she exhibiting?  X-rays after day 50 are the absolute best way to determine if your female is carrying.  It will also give you peice of mind.

Good luck