How long has it been since he last ate or drank anything?

I'm sorry, but you NEED to get this pup to the vet, even if you can't really afford it. Maybe they can sort out a payment plan for you, to make things easier, either way, he needs to see a vet. At least talk to your vet over the phone to see if there's anything you can give him.

Please keep us updated and let us know what happens!

EDIT - Has he been vaccinated? My JRT Ollie got Parvo when he was a pup, even though he'd had his vaccinations. He had the same symptoms as your pup, not eating or drinking, looking sad and weak, etc. We had to rush him to the vets at 3am, and the vet said if we hadn't of got there when we did, he would've died.

I'm not trying to scare you, but this is something really serious, especially as your pup is so young. He really, really needs to see a vet.