What Causes Excessive Itching On The Body?

I'm a 72-yr. old female and since a wk. ago I've experienced itchiness all over my body, no rash until I scratch, and I can't find a reason for it. Some ideas I have are an increase in Vit. D3, from 1400 IU to 2400 IU/day, adding Alpha Lipoic Acid to my regimen, for cleansing and inflammation (arthritis). Also, I've been eating salmon and other fish several times a wk. I'm part of a cardiologist sponsored group for healthy living, including exercise, healthy eating, etc. - since 7 wks. ago. I'm in ketosis, low-carb supplements from the hospital. What is going on? I have no rash, yet the itchiness is "driving me crazy". Thanks for your help.
Patricia Hammes