You may want to take him to a vet. The swelling could be fluid retention or caused by a bacterial infection in the intestines. It may be in pain and that's why it screams when you pick up your pac. I'm no expert by no means, but it could be Dropsy. The description is an abnormalAccumulation of serous bodily fluids. The causes are, possibly bacteria, but more so improper body metabbolism. This could be caused by an inadequate diet or poor climatic maintenance. Symtoms are, Bloating, soft dermal abnormalities. Particularly around the abdominal region. I just read this from a book I have. I would suggest taking him to a vet. Its too risky to treat at home. I'm not certain this is what's wrong but it definetly sounds very similar. Good luck. I hope he gains a full recovery soon.