My Dr. Checked to see if an infection bc complaining of tooth pain till dentist can see. She prescribed Antibiotics. How did she know just by seeing?

Guess. MDs know little about tooth problems. He/she knew that most toothaches are bacterial infections so antibiotics would treat you til you could see your dentist.
I'd like to know too. I usually use radiographs and vitality tests to insure a proper diagnosis.. no need to prescribe antibiotics needlessly. Your physician should have immediately referred you to a dentist for care.
See a dentist ASAP. Most medical specialists cannot diagnose many cases of toothache, they are not trained and competent in dentistry.