Licking his mouth can be a sign of mouth pain, nausea or sometimes a seizure. Check your dog's mouth for tartar on the teeth, possibly red gums, darkened teeth, broken teeth or something caught between the teeth or gums. If you find something stuck, try and remove it. If it is bad teeth, you can give him Buffered aspirin can be given to a dog with a dosage of up to 5 mg per pound every 12 hours. Keep in mind that a dog's body does not metabolize aspirin in the same way as a human and thus should not be given more than a day or two without contacting your Vet. The aspirin may need to clear your dog's system before other medications can be given, so keep that in mind if you decide to give aspirin and be sure and tell your vet when your dog is seen.
If you suspect it may be due to nausea you can try some Pepto-Bismol which can be given to a dog at 1 tsp per 5 pounds every 6 hours for upset stomach, gas, or diarrhea. Be sure it doesn't contain aspirin. Some Pepto-bismol does.
If your dog becomes uncomfortable, you should take him into the vet. If it is possible that your dog ate something toxic such as chocolate, cocoa mulch, antifreeze, medications they will need to see a vet immediately.
Now rawhides are no longer considered safe for dogs. If a large piece is swallowed without being softened first, it can lead to an intestinal obstruction, abdominal pain, vomiting and an inability to defecate. You can read about intestinal obstructions here:
This is usually considered an emergency, however, many vets if they know rawhide has been ingested will give it 12-24 hours to soften and move through the system on its own. Pancreatitis can also cause stomach pain, vomiting and diarrhea.
Symptoms of pancreatitis vary but include vomiting, diarrhea, anorexia, weakness or collapse, dehydration, shock, fever, depression, and upper abdominal pain. A dog may indicate abdominal pain by acting restless, panting, crying or wincing when picked up, shaking, standing with an arched back, or lying with the front end down and the rear end elevated
You can read about it in detail here:
If your dog starts vomiting, I would have him seen immediately at this point if you decide to wait to take him to the vet.
I hope you find this information helpful.