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It is possible that she has a uterine infection called pyometra. The signs of such an infection include any of the following:
Discharge from the vagina
Increased drinking and urination
Loss of appetite.
These signs typically show up 2-8 weeks following the heat.
If she has the discharge but is fine otherwise, it is okay to book an appointment for tomorrow or the next day to see the vet, but if she has more than one of the above signs, you should visit your local emerg. clinic.
Pyometra can be a life-threatening condition, and it is best to have her checked out to be sure. If it turns out that she does not have this infection, your vet can do x-rays or ultrasound to confirm or rule out the pregancy, as puppies are visible on radiographs by this point.
It is possible that she lost the pregnancy, but this far along, you would likely be able to recognise fetuses in the abortus. This unfortunate event would also leave her vulnerable to infection, so you should have her checked out in case she needs antibiotics.
I am still most worried about the possibility of pyometra.