Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I'm sorry to hear that your little one had diarrhea and is now vomiting, and shivering.
In most cases diarrhea and vomiting are triggered by eating something they should not, too much table food, too many treats or something they find outdoors.
More serious causes of vomiting include viral or bacterial infections, chronic pancreatitis, esophageal reflux, a dietary allergy or sensitivity, inflammatory bowel disease, internal organ failure (kidney or liver disease), a full or partial gastrointestinal obstruction or even infiltrative cancers such as lymphoma.
Because she is a younger pup internal organ failure and cancers are less likely but I mention them to be complete.
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 vomiting even water ideally she would see a veterinarian now. Young puppies dehydrate easily and she needs fluids.
If that isn't possible for whatever reason there are some things we can try at home, but we cannot replace in clinic intravenous fluids and injectable medications so if she isn't responding quickly she should see a veterinarian promptly.
To try and settle her stomach you can give either:
1) Pepcid ac (famotidine) at one half of a 10mg tablet per 10 to 20 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at one half of a 20mg tablet per 20 to 40 pounds of body weight every 24 hours
These are acid reducers and should help her feel better and hopefully stop the vomiting. They can be given for several days if necessary as they are quite safe.
I would pick up all food for now and water for a couple hours to allow her stomach to settle after the acid reducers. In a couple hours when you give her water make sure it is in small amounts only. If she drinks too much too quickly that can lead to vomiting. To get some electrolytes in you can also offer her a 50:50 mix of pedialyte and water.
If there is no vomiting for 12 hours offer a bland diet of 1/3 boiled minced white skinless chicken or lean hamburger and 2/3 boiled white rice mixed with some low salt chicken or beef broth to make it easy to lap up and swallow. If she refuses that you can offer a little meat baby food. If she refuses both then don't push it. She needs hands on veterinary care at that point.
But if things go well and she does eat and doesn't vomit feed her the bland diet for 2 to 3 days then slowly start to mix back in her regular food, a little more at each meal. It should take about 5 to 7 days to slowly convert her back to her regular diet.
If she continues to vomit, runs a fever (more than 103F rectally), has a tense painful belly or if she refuses to eat she should see her veterinarian for an examination, diagnostics, injectable anti-nausea drugs, intravenous fluids and supportive care.
Please let me know if you have any further questions.