You should be using Nizoral anyway. Not necessarily for the itching, but because the ingredient in it supposedly has a beneficial side effects of improving hair quality. I use it, and minoxidil, and rarely flake.
Give the Nizoral some time to work. For me, I noticed a halt to it within a week and a half. If your scalp is still bothering you, add in T Gel. T Gel feel gooooood. Others prefer T Sal, which is similar to T Gel but has a different active ingredient. Still others prefer good ol' Head and Shoulders, another option for you. Experiment and see what works for you.
Personally, after a LOT of shampoo experimentation I use Nizoral on Monday, Wednesday, and Friday nights, and cycle my normal non-medicated shampoo on other days. I apply the Nizoral, lather it in well, and then let it sit on my head for several minutes while I soap up and wash the rest of my body. Then, rinse out and apply conditioner. You will need conditioner afterwards, Nizoral as a shampoo is somewhat harsh on the hair.