[colesea]

you are going to take forever to cycle your tank if you continue at the rate you are going. Not only does medication destory the parasites, but it also destorys all your beneficial bacteria which you are trying to culture in your tank. Constant water changes and gravel vaccuuming are also hindering already delayed bacterial growth. Your tank is only three weeks old, two of which you've been medicating for. You probably don't have any beneficial bacteria in that tank yetl, which is why your ammonia and nitrItes are still climbing constantly.

I would return your fish to the LFS and do a fishless cycle. Do a 50% water change then create an ammonia source for the tank (either with commercial ammonia or by allowing a piece of meat to rot in the tank). Increasing the temperature to approximately 86oF-90oF (something I do not recommend with fish in the tank) and leaving the tank barren of life for four weeks will starve out the parasite without the use of medications.

One thing to keep in mind is that mollies and swordtails do enjoy a double dose of aquarium salts in their tank. Mollies are truely brackish water fish, and while many people may have them in fresh water without problems, this is because their tanks are already chemically stable and drinkable clean. Any fish in unstable conditions such as a cycling tank will continue to repeatedly get ich or other diseases because the chemical imbalances stress them out and leave them opened to infection. Mollies kept in fresh water are also more prone to get fungal/bacterial infections and ich than mollies kept in brackish conditions.

Good luck and lots of patience. You have a long (and seemingly fustrating) journey ahead of you.
~~Colesea