i agree with dosing with a different med. you'll want to make sure to match as many symptoms for the medication given, to be sure the right meds are being used.
the only thing i can think of, is that your fish and its sickness has become immune to maracyn because of the repeated use. perhaps the 5 day dose jusy wasnt quite enough to get it all, then after being picked on and becoming stressed, it was able to take hold again, perhaps this is why it has come back, and so strongly this time.
i do not have the knowledge to recommend a good medication (i have only used maracyn so far for my fish)
also for furure refernce, it is recommended to run the medications longer than what is prescribed on the box (box say 5 for treatment, i have run for 10, just to make sure i got it all) depending on the medication chosen, you can ask other members how long to use the product.
with any medication, keep eyes on water quality for some meds kill all bugs, good and bad.
you sound like you are doing a good job with your fish, i hope you can clear this problem up for good

-Toot