How do you wash your scalp? It may be the technique you are using. Make sure you are using your fingerpads to really scrub at your entire scalp when you wash. Just swishing the product around isn't going to help.
What you could try to get rid of the flakes is mixing in some brown sugar in your shampoo. This will exfoliate and get rid of the flakes hopefully.
For an itchy scalp, it often means that it's irritated, whether it's from products, too much itching yourself, or build up. So try to be gentle and rinse with cool water. Shampoos with tea tree oil in them are good for your scalp and they have a wonderful numbing sensation that will leave you itch free for awhile. A good one is Giovanni's Triple Tea Treat shampoo.
If none of that works, you could try doing oil treatments on your scalp. This may sound counterproductive, but itching is often a symptom of dry skin. Check your flakes. Are they white? Or are they green/yellow? If it's white then you have dry scalp, and rubbing coconut oil all over your scalp, letting it sit, and then washing out with shampoo, will work wonders. If it's green/yellow, you have dandruff and I would recommend seeing a skin doctor/dermatologist and getting a prescription to get rid of it.