I was thinking if it was soft and the legs were swollen also that it could of been edema but if its hard to the touch I don't think its that. He may have some sort of internal bacterial infection in which you will need meds from a vet to help him, or he could of contracted some sort of parasite from a feeder in which again he will need meds. Sorry I couldn't of been more help but it really sounds like he needs a vet and if you can t find one I don't know what else to suggest. Does he still eat?