For the past 3 days I've had what feels like a cold. At times I've been shakey and feeling quite weak but it's not that bad. I haven't had a stuffy nose or sore throat but I definitely feel a little bit sick. Since this started I've also been producing black poop. Aside from the colour it's completely normal, and not tarry in any way. I haven't been eating any differently at all, or consuming anything particularly dark. I've also never had anything like this happen to me before. Any idea what's going on?