Different staph and strep infections grow stronger everyday. Some Drs are really hesitant to prescribe AB because they are afraid they are contributing to building a "Super Bug". It might be they need to treat it with a different AB. Keep fighting. You are your best advocate. The Drs only know if you tell them and they listen. If you are not responding, keep pushing them or go elsewhere. Your mouth is a very dirty place and easily starts infections. You'll probably never answer the "how". I wish you well. Please let us know how you are faring.