I'd suggest getting some test kits and checking the water for Ammonia, Nitrite and Nitrate. If you didn't cycle the tank before adding fish, your tank will be going through the nitrogen cycle (there's a sticky on cycling at the top of the Newbie forum). Daily water changes are needed while the tank is cycling to keep Ammonia and Nitrite levels down and reduce fish stress.
As an aside, goldfish aren't going to fit into a 10g for long - they're messy fish that grow quite large, and require a lot of room to stay healthy.