Um not trying to scare you- but itching is considered a severe side effect. You might be developing an allergy to it. I had to stop taking it because my blood pressure became so low I was dizzy all the time.
Here are the side effects if you'd like to see:
http://www.drugs.com/sfx/spironolact...e-effects.html
I'd call your doctor but personally I'd consider getting off of it if the itching does not stop OR you notice you have any of the other severe side effects.