It may not matter anymore.
Sorry to be blunt, but this is not something you should be asking about on an internet message board, this is a veterinary medical emergency. You need to take him, RIGHT NOW, to the closest emergency vet because this does NOT sound good. Truthfully, you should have taken him the very first time he cried out in pain for no apparent reason because now whatever it is has had two more days to affect him negatively without treatment. Please don't delay any longer, take him IMMEDIATELY.
Ghilly
There is absolutely no way we could even speculate. He needed medical attention 2 days ago. Please don't let him suffer.
Hes is pain, won't eat, and has irregular breathing,what are you waiting for, take him to the vet. He could die quickly from dehydration at that age.
This is a medical emergency. He could literally be dying. Please get him to a veterinarian.
Poisoned? Please take the little fella to an emergency clinic. Is he drinking water? Dehydrated? Call the folks you got him from & ask if any others are ill...Poor baby. He is relying on you...don't let him down.