I'm sorry to hear you're still having trouble. Yes, you will need to keep doing water changes. The Melafix isn't going to work very well as long as there is ammonia in the tank. When a tank starts to go through the cycling process, ammonia is the first by-product produced. If cycling cannot proceed (as when a tank is too small), you're not likely to see nitrites or nitrates, just ammonia.
Since the ammonia isn't going down with only water changes, and you can't get a bigger tank, you may have to use a product that removes ammonia. Many aquarium water conditioners also remove ammonium. Ammonium is actually a form of ammonia with an ion attached. It is less toxic to fish than the non-ionized form of ammonia, but not harmless. AmmoLoc, Prime, and even AquaSafe all do this. They all contain a similar ingredient. AmmoLoc is sodium hydroxymethane sulfinate. AquaSafe contains sodium thiosulfate pentahydrate and Prime contains complexed hydosulphite salts. Note that each of these contains a form of sulfur, which is what causes the reaction to remove the unwanted chemicals. They all work in the same way. Many experienced aquarists believe that we use too many water conditioners and that such use isn't good for fish. They use the conditioners only to condition water for small fish bowls where complete water changes are done, when more than 20% of the water in a tank is changed at once, or when there is some kind of "disaster" in a tank. Your situation qualifies as one of those disasters. Here's where you can read more on the subject:
These products are not something you can use once and solve the problem. You'll have to keep using them regularly. This won't be good for your fish, but it's better than ammonia. The amount of ammonia you now have is enough to be fatal if you don't do something about it. So, yes, at this point I would recommend going to a pet store and buying an ammonia removal product such as those I named above. I hope that between water changes and the removal product you'll be able to get the ammonia down. If you need anything else, don't hesitate to ask.