Hi, If he becomes lethargic or you notice blood in the stool or vomit, he needs to see his vet promptly. As this is a sign of serious illness including a parasite infection or a blockage among other things. This sounds like a case of upset stomach. You can self treat this at home unless any of the above symptoms start presenting.I would recommend skipping his next meal and allow his stomach time to rest first. Make sure it is a couple of hours before his next meal. I would then start him on a bland diet of boiled chicken and rice to help settle his stomach.(1 part skinless chicken Breast to 3 parts white rice)
I am concerned with him becoming dehydrated as this is quite serious with dogs. I recommend giving him unflavored pedilayte to replace the electrolytes.
You can give Immodium or Kaopectate Here is a link with dosage instructions: http://www.peteducation.com/article.cfm?c=0+1459&aid=1432