You did not state you consulted a Vet. Did the Vet think you she needed an antibiotic and prescribe one ? Antibiotics should be used with caution in pregnant dogs as they cross the placental barrier and can affect the puppies development or worse. I have heard Baytril and Tetracycline should not be given. Have heard of Amoxicillin being used. I have only had to use antibiotics on a couple of my females post-whelping.
Depends on what you are treating and maybe no treatment is necessary.
Please understand that none of us are Vets here.
Under these circumstances, you should rely on the advice of a Vet as to what antibiotic would be the safest to use. There can always be a risk in pregnant animals.
If she has to be treated and you are concerned, you might consider a x-ray or ultrasound at around 45 days gestation.
Of course I consulted a vet! I was looking for a second opinion.
You really should be consulting a Vet to have her checked and see if she even needs medication.