Trying to narrow down what might be causing the following symptoms: - fatigue, in bed for past 4 days, dull nausea, feel as though I have been poisoned, constipation, feels tender deep inside left side, like there is some sort of obstruction, explosive diarrhea over the past 2 hours which seems to be giving me some relief. - background: male, 60, active, very fit, normally very active, so this is causing concern.