I am going to have to go off-line for the night as it is approaching 11:30pm here! But before I go, I wanted to leave you with some information as I am worried about your little Yorkie.
If she vomited several times and it was clear, then blood tinged at the end, I am much less concerned than I would be if she vomited a pool of blood. Also, if she has had bloody stool, or black and sticky stool (which would suggest digested blood), that would also make me very worried about her.
Given what you have told me I am concerned your girl may have HGE - hemorrhagic gastroenteritis. This is a problem that tends to occur in small breed dogs, often when they are quite young (2-4 years is most common). It comes on very suddenly, with vomiting, diarrhea and frank blood in the stools.
Typically, these patients are very dehydrated and shocky. A blood test called the "packed cell volume" (PCV, hematocrit or HCT are other names for this) is often 60% or higher, which is a measure of how very dehydrated and shocky dogs with this problem are. HGE needs to be treated aggressively with IV fluids, anti-nausea medication, antibiotics and gastric protectants.
In terms of what causes this, the short answer is we don't know. There are many theories - a virus, a bacteria, a food poisoning, a parasite, stress. The botXXXXX XXXXXne is that we really just don't know. Most dogs that have HGE never have another episode, however.
With treatment, most dogs do recover from HGE and have no lasting problems. It does, however, take several days of treatment and supportive care.
For more information, here are some links:
Now, I don't know that this is what is going on - it is the thing that worries me most because it is so serious. Given how much vomiting and diarrhea she has had, AND how weak she is and how uncomfortable her belly seems I do urge you to find an emergency veterinarian immediately!
I hope that helps you. If this has been helpful, please hit the green "Accept" button and leave feedback. If you need more information, just click on reply and I will still be here for another 10 minutes to provide it, or otherwise will be back in about 8 hours!
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.