I would go and see another vet personally. He looks kinda butchered to me and after 3 days he shouldnt still be whining. Ask for more pain meds at least to help him. If hes in a ton of pain hes not gonna want to eat. Thats a huge incision, much larger than needed. Im feel terrible that hes going through that. Also ask other vets about giving him a bath but my vet said not until about 10 days after surgery. I will pray things start to improve for him... poor guy