Your vet should become your best friend right now, as she gave you the best possible advice. Do not vary from any of her instructions. Hope all turns out well for you and Duke.
In a young dog like this when I hear "bloody diarrhea", my first thought is parvovirus. I know that you said he's up to date on his vaccinations but there is always an outside chance that a dog can still contract the disease even if they have been vaccinated. Did your vet test him for parvo?
Bloody bowel movements along with vomiting can also signify an intussusception. In an intussusception, part of the intestine telescopes back over itself, causing part of the intestine to have its blood supply cut off. If not surgically corrected it CAN be fatal. Careful palpation of the intestines will reveal a sausage-shaped mass, which is what the area of intestine feels like to the touch when it telescopes over itself. It is more easily diagnosed with ultrasound or MRI, however many small veterinary offices do not have these techniques available to them and must refer patients to specialists or larger, more modern hospitals for cases like this.
Please keep us up to date on how he is doing. Hopefully it will just be a bad case of gastritis and an intestinal irritation because of the worms.
Ghilly