If you change the filter every time you do water changes, you're removing all the beneficial bacteria that removes the ammonia the fish produce, so at this point your fish are swimming around in their own waste.
If you have a HOB (hang on back) filter you probably have floss cartridges, correct? The manufacturer tells you to change these just so they can soak you for the money to keep buying the bags. The way to do it is to just swish the bag in the old tank water that you remove when you do water changes, then just put it back in the filter housing. These bags will last for months and then will start to deteriorate. When that happens, just put the old bag into a new bag and put it back. This way you'll keep the beneficial bacteria. Better yet, buy a sponge to fit in the space and you'll never have to replace it, just rinse it out in old tank water.
You don't need to boil the water, just get a good dechlorinator such as Seachem Prime, which neutralizes harmful substances from the tap water.
Just waiting a couple of weeks before putting fish in is not cycling.
At this point you'll be doing a "fish-in" cycle, which will require daily water changes. Please read
here about fish-in cycling, and other resources for your tank.
Good luck, and please keep us posted.
