Suggest Treatment For Diarrhea

Hi school. I have a 15 year old son that has missed 4 days of school due to diarrhea for 4 days. I did take him to the doctor when he had just 2 episodes and an unsettled stomach. She feels like this might be a flu virus. It always is worse in the morning and then by evening it seems to stop. He does not have abdominal pain and no fever. Stool;s have no blood or mucous. Do I just let the diarrhea take its course or do I start giving him something to treat it? I am giving him bland food like rice and plain pasta. He was feeling great last night and had a small amount of pasta with tomato sauce and then had diarrhea this morning. Any thoughts would be appreciated.ing