Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Missy isn't feeling well, lethargic with vomiting, loose, and now bloody stools, lack of an appetite and extreme lethargy/weakness, shallow breathing, and feels cold to the touch.
She is likely dehydrated because she is vomiting and has severe diarrhea, but if even water is making her vomit you need to take it away from her for now.
In most cases vomiting/diarrhea is triggered by eating something they should not, too much table food, too many treats or something they find outdoors.
More serious causes of vomiting in puppies include viral or bacterial infections, a dietary allergy or sensitivity, congenital internal organ failure (kidney or liver disease), or a full or partial gastrointestinal obstruction.
In a young dog, especially one that hasn't finished her vaccine series, a viral infection such as Parvo virus or a foreign body leading to a partial or full gastrointestinal obstruction would be the most likely cause and both can be deadly. Not all dogs with viral infections run a fever initially, sometimes they are too weak to mount a fever response. Worms can cause loose stools, but rarely cause vomiting and lethargy.
Because she is young, this has been going on for more than a day, and she is lethargic ideally she would see a veterinarian now. She is a very, very sick girl given your history of extreme weakness and changes in breathing. Young puppies dehydrate easily and she needs fluids and her electrolytes rebalanced.
I know that this isn't what you had hoped to hear but she needs to be seen by a veterinarian on an emergency basis tonight. She is in real danger. Bloody diarrhea means that her gut lining is raw and that means that bacteria and their toxins can enter their bloodstream and she can become septic quickly, which can be deadly. It appears she is beyond home care.
I do recommend using external hear sources to try to help her get warm. Hot water bottles, microwaveable hot packs or wrapping her in towels out of the dryer could help. Dogs that cannot maintain a consistent normal body temperature are critically ill.
If you aren't sure where to find an emergency clinic here is a link to help you find one near you:
Best of luck with your little one, please let me know if you have any further questions.