Sounds like a stomach virus - but -
Hate to bring it up, and I know it sounds like I'm trying to make some gross joke - but watch your s***, man. Take the revolting time to examine it.
I mean that. If it turns dark and tarry looking, and has an unusually foul smell, get to the doc - quick!!!! When it does that, you're bleeding somewhere, and it needs to be handled before it perforates (goes clean through and dumps digestive bacteria and s*** into the abdominal cavity).
I'm no doc, and don't give medical advice, and all tyhe other disclaimer crap applies here.