I can't figure out why my dog has thrown up 12 times in the last 8 hours. Any suggesstions?

Most likely it has eaten something not good for it. Large doses of things like chocolate, or repeated small doses could cause it. I have also recently learned that small amounts of grapes or raisins can kill some dogs, but don't know the symptoms. This could be an emergency. I would try to get help even though it is Sunday evening. Morning could be too late. Start with any emergency number your vet has. Otherwise try the regular number, it may forward to a paging service weekends. If you don't get through, try to find an emergency number in the phone book.