Hello, I'm A 14 Year Old Girl. My Scalp, Ears,

Hello, I'm a 14 year old girl. My scalp, ears, back of neck and somewhat body have been itching very badly. I have a rash at the back of my head, lower. It's not lice, or bed bugs. I think it may be an allergy, but the doctor said that I just change my shampoo and i did and nothing happened. What do you think it could be?