If you are to have any chance of helping him, you MUST find a way to get him to a vet very quickly. Four days is way too long for a tiny dog like he is to go without nutrition. Plus, it's very likely he is dehydrated. Dogs who won't eat very often won't drink enough either, and if he's throwing up that adds to the dehydration problem. It is very possible he could even die of the dehydration alone. That is massively dangerous for a tiny dog.
I can't tell you what is wrong. It could be anything from kidney trouble, or pancreatitis,to infection, or it may be no more than a badly upset tummy. But he needs veterinary care immediately. No doubt the vet will need to do his bloodwork, to get a picture of how his organs are functioning. That is often a first line in diagnosis with dogs, as bloodwork shows up many things.
Of course, this costs money. Can you get "Care Credit"? (You would need to ask about this at the vet's office)
Otherwise, is it possible to borrow this money either from someone you know who trusts you, or on your credit card, or via bank overdraft?
There are some helpful resources someone posted here a while ago, for assistance in paying vets' bills. I'll see if I can find the post, and I'll be back with the link to it.
Take him to the vet straight away.
I am force feeding my 10 year old purred chicken and rice and also giving her pediliate.Is there any home remedy I can give her for stomach upset please help.she's been to the vet 4 or 5 times and I just can't afford it anymore