Does it look like fresh blood? Or is black and tarry looking? I've been led to believe that if it is blackish that the bleeding is typically in the stomach or intestines and if it is bright red then it is closer to the exit area. The vet can give you a medication that can coat the digestive lining that will stop any bleeding him might have. His symptoms sound similar to Hemorrhagic Gastroenteritis which the main symptom is usually an onset of bloody diarrhea in a dog that hasn't had any other health issues. Both of my dogs got this recently and instead of the diarrhea they both had blood in their vomit. Antibiotics will likely treat whatever the problem might be. I hope he feels better!
(I just noticed that Lady Montava on SM was responding to you, she was a great help to me when my two were sick.
