The left side of my head is really itchy.

The left side of my head is itching unbearably. I've been to several dermatologists, but nothing has helped. They say the itchy area doesn't show any symptoms... I've been using anti-hair loss shampoo for a long time, but can I stop using it? Sometimes, when I scratch the itchiness, I feel small, dead skin cells come off. What should I do?