How to reduce the itchy

I am female and I've got BN on my left arm. I realized this on 11 years old. Now i am 24 years old. This patch get always expand for last 3-2 month. I've read much about BN. There's no cure except using laser, but it has 2 sides too. It will bcome heal or worst. And now the patch soooo itchy sometime and become larger and expand around my arm and armfit. I've met a dermatologist, she gave me desoximethason 2,5% salf and cetirizine 10mg. But it just same. And i think my BN bcome more darker. Because the itchy, my body get assumption that all of my body get itchy too so i scratch and stricken my body. Please help me.how i supposed to do..... thank u..