Hello, I Took A Zpack For A Persistent Cold/infection That

Hello, I took a zpack for a persistent cold/infection that I had for 3 weeks. During this time I also took zicam oral tablets, one of which I took on an empty stomach the day after completing the zpack. That afternoon I developed stomach cramps. A day or so later I developed diarrhea which has persisted now for several days. I went to a walk in clinic and the doctor prescribed flagyl for a stomach infection but without doing any tests. Would you recommend taking the flagyl or waiting a couple of days to see if the diarrhea clears or go to another doctor and request testing for infection?

I am a male 52 years old weighing 190 in generally good health.