Please take your boy into the emergency center immediately. His condition could be related to multiple causes but my concern is the fact that he has not eaten in 4 days. Dogs who do not eat for this extended time can develop a condition called hepatic lipidosis or fatty liver disease which can be fatal without treatment. At this point he is most likely severely dehydrated. He needs to be placed on fluids and have a blood profile performed to rule out organic disease like kidney failure or pancreatitis. My initial concern is possible foreign body obstruction (toys, socks, bones, rawhides) or toxic ingestion like having access to antifreeze. There is nothing that can be done from home at this point. He needs to be seen.
Please let me know if you would like further information.
Theresa
A Voice for Your Pet
15 years experience in small animal medicine