Hello and thank you for your question. The use of plan B should not have any effect on your antibiotics prescribed after your breast augmentation. Contraception overall is a touchy subject and you should definitely speak to either your gynecologist or primary care physician when it comes to the details of which form of contraception to use. Otherwise, all of my patients are instructed to avoid sexual activity for at least two weeks in order to decrease any chances of trauma to the breasts that can cause bleeding, damage to the healing wound, and pain to the breasts. Hope I was able to answer your question. All the best! Alex Zuriarrain, MD, Plastic Surgery