If you can find an exotic vet in your area they will give a diagnosis
Three years is very old for a hamster so I don't think they'd be wanting to operate for any reason - it would be more a case of relieving symptoms and pain relief. Hopefully they will give you good advice and if they can treat you could ask about having some Metacam for pain relief as well. He's about the equivalent of 120 in human years
He sounds like he may be fading now and nearing his time. I hope things go smoothly for you and him xxx