It could be anchor worms - they are white and can be in the fin joint and are known to attack goldfish. You could try this product called "Dimilin" that you can purchase from watergarden.com and on that page you can read about this disease and see a photo of it so you can maybe tell if it's the same thing your poor fish have.
Are you o.k. now? 3 weeks is a long time to be in the hospital!
Did you have someone feed your fish while you were gone?
Next time, could you have a relative or a friend well-trained in advance to clean your fish tank for you, also, while you are gone? Maybe make friends at a petstore that has a great fish department! : )
