Why do my goldfish keep dying?

Question
I got 2 goldfish and a new tank with a filter they were very happy.We got another goldfish and they welcomed him into the tank nicely,but about 2 months later after we got them 1 died.He sunk to the bottom and curled up he was trying to move so we got him out and put him in a bowl we did not touch it but we tried to get him  swimming.At night we put him in the fish tank and he died late in the morning.About 1 month later my other goldfish is on the bottom on the tank curing up with his fine down he will swim to get his food and when the other fish try's to help him.Please help me I don't no what to do!

Answer
Amelia,
What size tank are your goldfish in? How often do you do water changes? What size filter do you have? Do you place new fish into your hospital tank for 2 weeks before you add them to the main tank? What are you feeding them? All of this is very important because I cannot see the fish. I can better help you when you get back to me about my questions.