Dear doctor, my sister has been feeling under the weather and having stomach pain/diarrhea for a week, and now her tongue is white. possible causes?

Evaluation : Your sister needs to see a doctor. Many causes possible: kidney stones, infection, bowel obstruction, appendicitis, diverticulosis, flue among many others. Take you sister to a doctor now.

White cost: On the tongue can be from the layers of plaque that accumulate daily. Make sure that and is brushing both her tongue and teeth twice daily. They sell specifically designed tongue brushes which you can use with water or specifically formulated gels. Hope this helps.