Hi, Welcome to Health care magic forum.
As you describe, it may be the side effect of the drug, may be due to the destroying normal gut flora
Or it may be due to the irritating effect of the drug.
I advise you to consult your doctor.
I usually prescribe to my patient with such symptoms lactic acid bacilli, ranitidine
, and ask to stop the drug macrobid
Wishing for a quick and complete recovery. Thank you.