If your son has been adequately treated with antibiotics, then it is better not to repeat the same again as it would cause more harm than good to him.
Please give him plenty of fluids orally. In addition, do not give him any other medicine either.
Make him eat lot of fruits and vegetable salads. If the ear and mouth infection is not subsiding, a skilled ENT specialist
can help him by doing an examination, swab culture and treating him accordingly.
Hope this helps.