Hello. My Son Is 21 And Had The Flu For

Hello. My son is 21 and had the flu for possibly a week. He has gotten over the diarrhea and nausea/ vomiting but still has a non productive cough and very tired. He says he is having heartburn type symptoms when trying to eat or drink. He is also experiencing swollen gums and minor tongue sores( like too much salt sores on tip of his tongue) and very chapped lips. Vital signs have been checked and within normal limits. What would you suggest?