I have to disagree here on using toxic DTHP products when prazi is a much safer alternative for flukes. Its not that DTHP products wont work but its equivalent of putting out a match using a fire engine hose and should only be considered when nothing else has worked.
As it has not been mentioned, any chemicals in the tank (copper/malachite green) need to be properly removed before even considering switching meds or you risk lethal interactions.
Can you please post your tank size along with with your stocking? Exact numbers for ammonia, nitrite, nitrate and ph? What your using to test (liquid or strips)? How long the tank has been running? The last time you added new fish? Before even considering any further meds, water concerns need to be addressed first here to rule out possible problems.