Welcome to HealthcareMagic. The kind of problem you are facing,from what i could understand is that you have itching around perianal region. Well its cause can be various like having a fissure, a fistula, a pilonidal sinus
You might even be having worms, for which you said you are already under medication. But i would suggest you consult with a surgeon/ proctologist
as well, get evaluated and then treatment.