You have pretty much killed your fish with all that medicine!! It's really, really not a good idea to be over-treating them, as their immune system is destroyed. Now, your fish probably has an internal bacterial infection.

Not to mention that your tank is not big enough for even one goldfish, let alone two. You need to have 40L per goldfish, in other words, you need an 80 liter. These fish of yours will most likely get sick and be unable to recover due to pollution in such a small environment.

I think you should actually get this fish out of his misery... OR treat him with medicated anti-bacterial food as a last resort. An injection of antibiotics would be great, but I do feel that it's too late already. There are a few humane ways to help a fish out of their misery, for example, you could cut the spinal cord (right behind the head) with a sharp knife, and the fish will die immediately. You could also separate the fish in a bag or bowl that you'll place in a dark freezer for a few hours. You should absolutely NOT "check on" the fish while it's in the freezer, as this will only stress him.

Please get a bigger tank for your moor if you want to keep him after this! And in case both fish survive, buy a 100L!!