Hi I went to an ENT doctor 2 weeks ago because I had white pus on my tonsils. He took a throat culture for strep and told me to start amoxicillin 875 mg twice a day for 20 days. Although my strep culture was negative I m not sure if gargling with a combination of salt water, listerine, and therabreath mouthwash might have altered the culture. So far it is day 11 on amoxicillin and all of the white spots on my tonsils are gone, my fever is gon, and my lymph-nodes are not as swollen. However I feel as if I have a canker soar or an ulcer in my left inside cheek right under my jaw. The pain is excruciating. Can amoxicillin be a cause of this sore and should I discontinue the use of this drug? I also am on a probiotic once a day 4 hours apart from my antibiotic intake.