I had fever, bad cough, pain and chills for a week?

60 year old male. I had fever, bad cough, pain and chills for a week. Now all back to normal. But during the week I
had diarrhea. Now after the fever and symptoms have subsided I continue to have diarrhea.

What can be the cause of the diarrhea and why do I still have it?

What can I do to stop the diarrhea?

Are there any tests that I should do?

Is the diarrhea a sign of a another problem?

I take no meds other than synthroid for thyroid and (low-dose) pills for high blood pressure.

I have had colonoscopy done once every 2 years – all OK.