My dog won’t eat..

The past 3 days/nights my dog hasn’t ate hardly a bite. Me and my fiancé have been thinking it’s the food but it’s the same food they’ve ate for the past 3 years and ontop of that, my other two dogs are gobbling it up just fine with no issues. He has thrown up a couple of times and he’s hardly drinking any water. We are unsure what to do at this point..any insight?