Amoxicillin is a form of penicillin, which is an antibiotic that treats numerous bacterial infections such as strep throat. Tell your doctor about all the other medications you are taking and any allergies so he can make sure amoxicillin is right for you. According to MayoClinic.com, a sore mouth is a mild and common side effect of the medication that does not require medical treatment and usually goes away on its own after a period of time.
Avoid foods and beverages that are hot. Also avoid spicy and salty foods and acidic citrus fruit.
Eat popsicles and gargle with cold water to help ease mouth pain.
Take over-the-counter pain relievers like acetaminophen and ibuprofen.
Rinse with salt water if you have a canker sore. You can also combine equal parts hydrogen peroxide and water, apply the mixture directly to the sore with a cotton swab, then lightly dab Milk of Magnesia on the sore three to four times daily. This mixture is soothing and might help the canker sore to heal, notes PubMed Health.