HI ! Possibly the infection in your abdomen is still persisting even if the symptoms were relieved at the first instance. There may not be any relation of your Plan B treatment with the diarrhea. I would suggest you to see your family physician, who may advise you for a stool test, and may prescribe some anti diarrhoeal along with a metronidazole preparation which may also help you in your GERD. Wishing you an early recovery.