After the first day - A vet should had been your first Thought - And there are a number of causes- None of witch will simply go away - I think of my pets as my kids- If this were your kid- Would you wait 3 days and ask here?
How can you let your dog go 3 days without medical attention!!!!!!!!!! You, yes you, are the one that can help your dog! It surely can't get medical attention by itself. Lets see you go 3 days in that condition.