I'll take a stab at this.
First, we need more info - what kind of fish, size of tank, and most important, your water parameters - temp.
NH3,
NO2, pH. How long had the tank been set up, what problems you had before, etc.
Also, how long have you been using parasite clear? How many doses? Also, how much salt have you added?
Notice anything on the fish? spots, dots? fins clamped? breathing fast or gulping for air?
Itchy fishy is most likely an external parasite, and commonest is ich. If you haven't read Allivmar's article on ich, you can find it in the articles section.
Most common prob with treating ich is not treating it for long enough. Ich goes through a complex lifecycle, and to treat sucessfully, you need to maintain treatment for 2+ weeks (depends on temperature). A single dose of parasite clear is not going to do much. (I suspect the package instructions will say "treat once & forget" like the Ich-clear I once used before I knew better. Don't believe it! You cannot treat ich with a single dose of anything..)