ugh i cannot figure out what's wrong with my three year old he was acting normal & fine up till…

ugh i cannot figure out what's wrong with my three year old he was acting normal & fine up till about an hour ago now he won't stop whining/ crying & won't eat anything or drink he is not acting himself acting like he don't feel good . no fever he coughs once maybe every hour .i hope he's not coming down with something .