Very likely because he is ill with a virus or systemic infection that may very well need medical attention!
Vomiting and diarrhea are signs of either a parasite overload with worms, protozoal organisms or bacteria. It can also be a sign of severe pancreatitis due to your pet getting a highly fatty treat or meal, or getting into the garbage, or being fed table food. Foreign body obstructions can cause severe vomiting and diarrhea if your pet has ingested ANY kind of material that is not digestible and that gets "stuck" in the GI tract!(rawhides, toys, plastic, paper, bones, mulch, etc.) With dogs, we always have to consider toxic exposure due to ingestion of medication, chemical, or product not intended for pet consumption. Finally, systemic disease due to kidney, liver liver failure, or cancer can cause vomiting, diarrhea, and chills in a dog. The shaking you are describing is likely due to a fever or from your pet being in PAIN or from being hypothermic or having a dangerously low body temperature.
All of these problems are potentially serious, so it would be very wise for you to seek veterinary assistance for your pet immediately today! IF you act early enough, you may truly be able to stop things from going from bad to worse!!
Your vet will likely want to do a baseline of testing on the feces, blood, and urine to try and pinpoint exactly why your pet is so ill. Hospitalization may be necessary, so please be prepared for that!
Don't wait all day to get your pet to the doctor. You will BOTH feel better once a doctor can determine what is wrong and begin supportive treatment!
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