I was not prescribed an antibiotic after my breast augmentation, is this normal?

You probably got a dose of an antibiotic through your IV prior to surgery which is usually sufficient.  Also, studies show that the incidence of infection with breast implant surgery is extremely low, with or without an antibiotic.  I am one of those doctors who gives patients antibiotics following breast augmentation surgery but it is probably more precautionary than anything.  I wouldn't worry about it.

In scientifically legitimate studies there does not appear to be any benefit by giving antibiotics to breast augmentation patients in uncomplicated situation. Most plastic surgeons do administer antibiotics, at least at the time of the operation, without any scientific justification.

Congratulations on having undergone the breast augmentation procedure. No, you do not have reason for concern. My practice has also changed; postoperative antibiotics have not thought been found to be necessary and are  therefore not utilized.

 Best wishes.