Your scalp ph may be all out of whack. I had the same problem and this helped.
Try taking a 1 liter soda bottle, filling it with 4 tablespoons of Baking Soda and warm water. Shake until Baking Soda is dissolved. You can put it in a smaller bottle (like an old lotion pump bottle). Run water on your hair in the shower; then, use this solution like shampoo. It is very watery, so you'll have to use more than you would a regular shampoo. (Keep your mouth closed; it tastes vert salty!) Massage the scalp and rinse thoroughly. Dry and comb as normal.
If you want a rinse that will complement this "shampoo", take another 1 liter soda bottle, fill it with 4 tablespoons of Cidar Vinegar and water. You can either rinse the Baking Soda out first, or put this "rinse" in right after you finish messaging your scalp.
Try this for about a week or so. If your scalp ph is out of whack, this will return it to normal. You will notice your dry itching scalp gets relief. It also makes you hair feel very clean, soft and easy to manage.
Hope this helps.