Long history of IBS but this is different - 3+ weeks of frequent and urgent watery diarrhea (not c-diff -checked), nausea, vomitting yesterday, very diminished appetite, weight loss of ~5+ pounds, very fatigued and feel weak. Drinking watered down Gatorade with benefiber, some relief with peptobismal tablets but that led to constipation and increased abdominal pain. CBC was normal last week except for slightly low potassium. What is your differential diagnosis and what else should I be doing? (I am an FNP, btw).