Hi, Lab studies are to be done. if I will be your treating physician, I will order stool culture/ova, parasite analysis and, fecal smears. Metronidazole is reported but can cause proctitis/anusitis as your history indicates. However, the above simple tests are still useful to rule out [as some diseases cause similar symptoms more often] Acute cases can be self limiting and require supportive therapy [hydration, if needed anti-diarrheals, or 5-ASA enemas] antioxidants vitamin a,c,e can be taken for few days, I will also suggest [deep breathing exercise or guided meditation by art of living course ombw or sahaj course will take away psychological stress and helps increasing success rate with medication]. It should be checked by physician once and then if medicine or surgical requirement needed can be taken. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sunny Madar, General & Family Physician