Let's do 2 more rounds of Prazi only 4 days apart with no removal of Prazi and no carbon in the filter during this treatment:
Day 1: Prazi 1
Day 5: Water Change then Prazi 2
Day 9: Water Change
If you have a heater, a temp between 75-78 degrees speeds up the Fluke lifecycle which ensures that the hatching larvae are killed by the second round of Prazi. Just raise the temperature slowly so as not to shock the fish.
I would do one more round of Prazi. Feed him once a day. Don't worry about his shyness, but do watch for frequent bottom sitting. If he is constantly bottom sitting, there may be a secondary infection which will require antibiotics. You may also want to do 2 weeks of salt at 0.3% after the 4th round of Prazi to be sure you've eliminated any other parasites other than Flukes. You can start the salt at 0.3% with the 4th round of Prazi if you double dose the Prazi.