The swollen belly may be an indication of a birth defect that is keeping him from thriving. Dogs have large litters and not all live to grow up in the normal course of things. He could have a heart, or liver, or kidney defect.
The pup may have ingested some thread or string or something from its bedding that is impacting the gut.
The pup may have a more severe than normal infestation of worms.
He could have a problem where his bowel is twisted or telescoped in on himself too.
Unfortunately many of the problems are things that do need vet care if the pup is to survive.
About the only thing you can home treat is if its worms and the poison in a worm medicine might kill him if he is as sick as you say.
You can try stimulating him by rubbing with a damp facecloth and try to make sure you stimulate him to eliminate. Do not feed him if he is chilled as that will leave him with food that will rot in his stomach instead of being digested. If he feels cool to you warm him by letting him sleep on a low temp heating pad or near a hot water bottle. Make sure he can get to and away from any heat source easily so he can regulate his temperature.
Its likely though that you will lose this puppy without vet attention and you may lose it even with vet care but unless you have a vet look at it you won't know if you could save it or not.
Some pups you can't do anything for - nature seems cruel but not all pups make it.
Hope this helps you - and good luck with the puppy!

---

Please press Accept if you find my answer helpful. Want more info? Just reply on your question!
Bonuses for good work are always appreciated!
Thanks for the opportunity to help you!