Most soaps and cheap body washes tend to dry out your skin. Try using a good moisturising body wash and after you shower remember to moisturise.
Also I used to get really itchy arm pits after I showered and I found out that it was because when I shaved under my arms I was cold and I had goose pimples. So shaving when cold irritates the skin.
Hope that helps : )
Switch your bath products to a more sensitive care range and while your doing this for any outbreaking of itching the Bach Flowers Rescue Remedy Cream is a god send for helping itching to stop