I agree with nabi! (As per usual...) if one medication isn't working, you need to change because it might sometimes even be a case of wrong diagnose even.
And for the future, in case you're worrying about overstocking (which I don't think you have), you should change water every single week, and at least 50% when keeping goldfish. Anything less is plus-minus zero since they create such incredible amounts of waste.
A quarantine tank of 10+ gallons would be a good investment in case you want new plants or fish in the future and want to avoid getting your goldfish family sick