There are several issues to consider when abdominal pain is involved as it can also be referred pain from the back or more serious issues like a foreign body and even pancreatitis. For gas pain you can actually give him simethicone infant gas drops which you can buy at your local drug store. However, if he doesn't improve a trip to the vet is needed to rule out the above serious conditions.
Dosing for simethicone would be about 30 mg and up to 60mg if needed. I would only do a one time dose to see if it helps.
I would also suggest pulling his food for 12 hours after his last vomiting episode as well then starting him on a very low fat diet. You can pick this up from your vet. Royal canin low fat or EN low fat are my recommendations. If you don't want to try the rx diets you can feed boiled white meat chicken and rice as an alternative. Keep his meals small and frequent for a few days and after about a week you can start mixing his regular diet back in.
I do want to emphasize that he should see a vet if his symptoms do not improve quickly.
Please let me know if further assistance is needed.