You might have a yeast infection, it's like athlete's foot or diaper rash. Has anyone done a fungal or yeast culture. Stop using deodorant and soap for a while, and pat cornstarch after drying, and see if that helps.
itching skin coupled with unusual stools can sometimes indicate liver problems. bloating? swollen eyes? sensitivity to certain foods? like yeast? definitely should get your bilirubin, albumin, AST and ALT (all liver hormones, enzymes, etc). these tests are all included in your standard CBC and Metabolic Panel blood test.
Have you been to a doctor? If not go and see if it's some kind of skin condition, or try changing deodarent/ soap, it might also be a bacterial or fungal problem. I remember a little while ago I got itchy armpits eventually it went away but I used talcum powder and that stopped a lot of the itching. Unless you were prescribed the cortizone by a doctor, I know some cortizone creams are not meant to be long term as they thin the skin area that they are applied to. Good luck