My Lady just had HGE on Memorial Day and her symptoms were very similar. She started with just a little upset tummy and not wanting breakfast to bloody diarrhea about four hours later. I rushed her to the vet. Fortunately, I got her there quickly enough that her case was mild and she didn't have to be hospitalized. HGE can become very serious and life threatening quickly.
Hopefully this is not what you are dealing with, but everyone should be aware of the symptoms. Toy dogs are prone to this and acting quickly can save their life.
Hemorrhagic Gastroenteritis (HGE)