Thank you for that information. I would stop using the flea shampoo as it may be drying out the skin which is causing the itching. There are several things to look at when it comes to scratching. Allergies to food, air or flea, mange,fungal infections, bacterial infections, or yeast infections and the only way to determine mange, fungal, bacterial, or yeast is to have a skin scraping done by a vet and each would require a different treatment.
If it is an allergy to food then you will see a rash on the belly or inner thighs as well , if it is an airborne allergy you will likely see her licking the paws causing redness, scratching and possible runny eyes. Dogs can develop allergies at any time in their life. Seasonal allergies such as grass, pollen, dust, dust mites, ragweed are more common allergens, but anything a dog can breathe in can cause a problem.
When it comes to food, then chicken, corn wheat, lamb or beef can cause major problems. I would suggest you take the dog in for exam to determine the cause and that you stop giving baths in anything other than oatmeal baths for dogs and you can use pure aloe on the rash to sooth it.
I would also recommend you start adding omega fatty acids to the dogs diet daily which will help to build the skin and coat and can help with allergies. I sue fish oil which works well. But here is more on this and options.
Omega fatty acids
puritans pride fish oil:
Dr foster smith skin and coat tabs
Benadryl had been known to help with the itch. You can read precautions and dosing here. http://www.petplace.com/drug-library/diphenhydramine-benadryl/page1.aspx