If your dog shows symptoms of stomach ache, make him rest don't disturb him, try avoiding food for 24 hours that may make the situation worse, if the symptom still not improved get him checked by a vet. provide him clean drinking water and keep an eye on him, if he vomits just after drinking water contact the vet as soon as possible, if not let him drink freely. If after following the first two steps mentioned earlier your dog feels back to normal provide him simple food that is easy to digest.