If the fish is not egg bound, unlikely given the time elapsed from the first post then I'm going to suggest you probably need a fish vet at this point for a formal ID.
If the scales are not sticking out (looks like a pine cone from above) then possible dropsy can be ruled out. Dropsy is indicative of liver, but usually kidney failure when the fish can no longer osmoregulate. They blow up like spikey balloons
Cysts, whether cancerous or not (both types) can trigger the symptoms you see too. Whilst a member here arranged for such a cyst to be debulked/removed recently, it was very much external as opposed to overall inner body swelling.
Given pics and your posts, I'd suspect a tumour If the fish is still swimming and eating, give him some grace. Quality of life still exists for now.
Euthanasia eventually may be the kinder option if struggling. There is a very helpful article here, painless and very kind for both you and the fish, if needs be.
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