You really need to get the puppy to the Vet and soon as they can go downhill quickly. Could be Parvo, parasites, etc.
Call your animal rescue & tell them you need to get your puppy a Vet appointment immediately! This sounds like Parvo to me & the smell would confirm it!!! Three days is too long & Parvo is fatal!
Dehydration alone, can kill a puppy.....Please, make the call now & get going...Please, let us know what happens...I hope it works out for you both! Karla
Yes , yes , yes , everything Misfits4me says.
If you can't get in touch with the animal rescue organization , leave them a message and take puppy to a vet ASAP.