Can he take pedialyte? I would start that and ask to see a pediatric GI. it sounds kinda like reflux... well the 6 month part. I hope that helps. But in the mean time I would take him to the ped to see if it is a virus or something else. Also watch for signs of dehydration.
It could be he ate something or has a virus, make sure he is drinking plenty of fluids, not milk give him water or soda for the electro lights, and he is better not eating till the vomitting stops, then give him light food ,chicken broth, boiled rice with a little egg is okay ..If it continues it is better to get him checked out at the Doctors. Good Luck I hope he is better soon .It would be good to get the cough checked out aswell