How do I know the difference between vomit and spit up?

Destiny
My son been having tummy troubles and I wanna make sure he's not sick. He's not running a fever or anything but it seems like he may be vommitting once a day. I'm not sure though. He drinks between 50 to 80 ml of formula. I've tried giving him less , sitting him up, and I've been giving him gas drops. I'm not sure what else to do.