Unfortunately unless you can find a vet who is able and willing to do major surgery (and they are out there, but few and far between; since you are in Singapore you MIGHT be able to find a Koi Vet who can do it - they are practically unknown here in the states), your fish will not survive. That is not simply a swollen abdomen; your fish has a large tumor which is obviously affecting the stomach and swim bladder. The poor thing is obviously suffering tho; if you cannot find a vetenarian willing to attempt surgery, the fish is only going to get worse.
There is a slight possibility the tumor is actually infested by some sort of parasite or is a very large infection (that small open wound makes me wonder), but if he hasn't eaten in 2 weeks, he is extremely weakend and the chances of him surviving medication is pretty limited, much less surgery. And since its near impossible to determine what the tumor IS, recommending meds will likely make the poor thing suffer even more.
Sorry chaoz; I know this is not what you want to hear, but sometimes the things we need to do for our fish are not easy.