I Have Very Itchy Left Nipple Only And My Left

I have very itchy left nipple only and my left arm pit is sore. I have not changed any from soap to food or tight clothes I have had this now for three weeks and not getting better. My nipple is not crusty or inverted I do not have any rashes I have no cold, fever, or flu symptoms no night sweats nothing except the pain and itchy. My whole left breast is also sore. I have not done any weight lifting or over stretched the muscle thanks Greg