I get canker sores during my period r which go away on their own usually . but this time the sore is severe near the gums and on one side of my throat - doctor i visited prescribed amoxicillin though i tested negative for strep - any advice ?

Canker sores are not bacterial infections & thus antibiotics are ineffective treatment. Try ice applications,rinsing with maalox or dabs of milk of magnesia. Ask your pharmacist to recommend a topical anesthetic suitable for oral application such as benzocaine. These should only last about a week.If no improvement, consult an oral surgeon.

Canker sores are caused by virus, not bacteria. Antibiotics are used to treat bacterial infections, and therefore will be ineffective. Please see your Dentist or an ENT for examination and appropriate treatment. And know that what you are calling a Canker Sore may be one of the hundreds of other oral lesions, most benign.