Is it possible that ive developed oral thrush from a course of antibiotics (flagyl) ?

Yes, possible: Metronidazole (Flagyl) and other antibiotics sometimes trigger yeast infections (thrush). All humans normally carry yeast on their skin and in body cavities. When antibiotics suppress normal, healthy bacteria, yeast can grow and cause symptoms. Usually it's easily treated and not serious. If you think you have an oral yeast infection, speak with the doctor who prescribed the metronidazole.