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Since it is occurring on specific areas, it has to be something that you are coming in contact with. Most likely if it was something you were eating that you were allergic to it would be more widely spread.
If you have recently changed any products, shampoo, soap, lotions, cleaning products, laundry detergent etc then change back to what you were using before. If you have not changed any products you may have developed an allergy to one. Slowly start changing your products. Start with soap first, get one that is hypoallergenic and free of perfumes, dyes and chemicals. Hopefully you will find something that changes your symptoms.
Another possibility is dry skin. Make sure you use a good lotion or cream at least once, preferably twice daily. Again, look for a hypoallergenic one. You can mix a little bit of hydrocortisone cream in with your lotion. Try taking a bath in an oatmeal soak, Aveno makes a great one.
You can try taking Benadryl before bed at night since the topical creams are not helping. It may make you drowsy the next morning. Take the instructed dose on the bottle.
If after trying these you are still having the symptoms, you may want to see an allergist or a dermatologist. They can do what is called a patch test, and this will let you know what types of things you are allergic to.
If you have any further questions please let me know. Hope you find the cause of your itch soon. Have a nice day.