Ok, i'm going to start by saying i'm not very experienced here. I've only been keeping fish a couple of years and there are people here who have been keeping fish longer them I've been alive but I have learned a huge amount since joining this site so I will share what I know in a nutshell until someone else steps in because I feel very bad for your fish.
1. The tank you have is way to small for those fish. From what I know about gold fish, yours will grow to 10 inches or more. Plus goldfish are super dirty fish so need more water and more filtration the others their size.
2. Have you cycled your tank? There is a great section on this site with all the instructions you need to go through this process and a ton of people to answer any questions.
3. You haven't changed your water yet? Even in a cycled tank water should be replaced by about 20% at least once a week. But in an uncycled tank your looking at water changes once or twice a day.
Now for what might be going on with your fish. Once you read the cycling information it will make a little more sense but I'll try to explain. Fish create waste (pee, poo, co2) this waste crests ammonia. Ammonia burn fish kind of like acid. Cycling builds bacteria to convert ammonia to nitrite which makes it hard for o2 to travel through the blood stream. The cycling also creates bacteria to convert nitrite into nitrate which isn't as harmful in smaller amounts but if left to build up it can harm. So that's where the weekly water changes come in to get rid of nitrate.
So basically, and anyone correct me if i'm wrong, the extreme amounts in your tank right now and causing your fish to become very ill and most likely near death.
To save your fish you really need to start changing your water. Asap!