You could be missing something in your diet or you could have developed an intolerance:
1. Zinc, Vitamin A and Vitamin D are needed for skin health.
2. Do you use a flaxseed or fish oil supplement? Lacking Omega's could cause itchiness.
3. Try an elimination diet, try eliminating wheat/all grains, milk, corn and derivatives, nuts, tomatoes, shellfish, cheese, soy products, citrus, caffeine, eggs, potatoes (I know all that is left is meat, fish, chicken, vegetables and fruit). Most people are intolerant to wheat and milk. After all these foods are eliminated for at least 1 week, introduce each food for one day and see which one gives you the problem.
4. Try bathing or showering without too much soap.