Getting Rid of Dandruff Flakes

I just hate seeing my visible dandruff flakes in my hair. I had tried using different anti dandruff shampoos like Head and Shoulders, Clear and Nizoral but still it doesn't work for me.

I had this Red, flaky, and greasy patches of scalp skin and its so itchy. I was searching online on what causes my dandruff flakes and I had found this out in Medical News site.

Here are some causes of my dandruff flakes:

• Dry skin - people with dry skin tend to get dandruff more often. Winter cold air, combined with overheated rooms is a common cause of itchy, flaking skin. People with dandruff caused by dry skin tend to have small flakes of dandruff; the flakes are not oily. 
• Seborrheic dermatitis (irritated, oily skin) - People with seborrheic dermatitis are very prone to dandruff. Seborrheic dermatitis affects many areas of the skin, including the backs of the ears, the breastbone, eyebrows, and the sides of the nose, not just the scalp. The patient will have red, greasy skin covered with flaky white or yellow scales. 
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• Not enough shampooing - some people say that if you don't shampoo enough there can be a buildup of oil and dead skin cells, causing dandruff. However, many experts doubt this is true. 
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• Reaction to hair/skin care products - Some people react to some hair care products with a red, itchy, scaling scalp. Many experts say that shampooing too often may cause dandruff as it can irritate the scalp. 
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• Diet - Some experts say that people who do not consume enough foods that contain zinc, B vitamins, and some types of fats are more prone to dandruff.  
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 and Here's what I Should do to Prevent it:

Before using an antifungal shampoo see if you can remove any scaly or crusty patches on your scalp - do this with care. If you manage to remove them the shampoo will be more effective.

Ideally, select a shampoo that has one of the above ingredients and shampoo your hair with it every day until your dandruff is under control. When that happens use them less frequently. You may find a particular shampoo stops being so effective after while, if this occurs switch to one that has another ingredient.

Make sure the shampoo has time to stay on your scalp before you rinse it off - perhaps about five minutes. If you rinse it off too quickly the ingredient will not have enough time to work.

I will try to look at some other brands of anti dandruff shampoos but If after several weeks of treating myself and if I  still have dandruff, I think I should consider seeing a dermatologist.