Hi.. Can understand your concern.. As per your complain sores in mouth when starting a new medication can be most probably due to allergic reaction to the medication, however other causes can be Stress, Nutritional Deficiency [Iron, Vitamin B12 and Folic acid] , hormonal changes, acid reflux, tongue trauma due to some sharp teeth or tongue biting habit, excessive intake of sour and citrus foods, uncontrolled diabetes and other immunocompromised conditions etc.. In case if it is allergic reaction to medication stopping the intake of medication and changing to other drugs and taking benadryl can help.. As of now to relieve pain you can gargle with numbing mouthwash containing Lignocaine especially before meals.. Do warm saline gargles.. Gargles with 1:1 solution of benadryl and milk of magnesia can help.. Apply numbing gel over the sore for relief from pain especially during eating.. Take a multivitamin tablet for a period of 15 days.. Avoid spicy, sour and acidic foods.. Hope this information helps.. Thanks and regards.. Dr.Honey Nandwani Arora..