this was happening to my dog a lot too; for 2 years; and was rushed to the ER 3 times for vomiting blood. it might be the food or the ingredients in the food. i was feeding her the honest kitchen and halo holistic before that; sometimes those food are not the best for a dog with digestive issue. anyway, no one can diagnose my dog until this thanksgiving; last visit to the ER the vet suspected IBD and my dog was put on purina pro plan lamb and rice. thank god she has been fine since then; she threw up only twice bile from empty stomach. i am not sure what the procedure of diagnosing IBD but Deb (dwerten) has more info about that. i think it might be the food. also my dog doesnt get any more treat or anything else but her food. (read my posts for more insight)
best of luck
what are the ingredients in the current food you are feeding?