Itchy nipple

I am 43 years old and female.
For most of my life my left nipple has been CONSTANTLY itchy.
From young teenager to nursing mother to full-on adult, this has been a noticeable anomaly, and I cannot remember it ever NOT itching... it's just a matter of...

the DEGREE of itch.
I have no discharge, no flaking, no relief from anti-itch creams, I do not wear a bra (not enough breast to hold one down!) and have ruled out detergent residue as a cause- for only one nipple is ever itchy and I have used too many different detergents over the years to not have noticed a change if there was to be one.
The only redness and swelling that occur is from me constantly scratching, and it is localized to the nipple. It is very embarrassing sometimes in public, to walk around with one nipple erect (from surreptitiously scratching!) and on more intense days is absolutely driving me bonkers.
What on earth could be causing this if it isn't the usual culprits of cancer/eczema/residue? Is there possibly a hyperactive nerve or something? I am between doctors at the moment, and previous doctors have not really had an answer other than it is peculiar to only me...
I have read posts on other sites, and no-one seems to have quite my circumstances, and so I am fishing here for others who might know what I have been dealing with most of my life.
Thank you for any help/relief that may be forthcoming!
Goodbye,
Ruby Tuesday
(and yes, that IS my name...)

I'd like to give you a direct answer, but it does seem that you looked at all the obvious possible causes...here's a few more to consider though:

Clothing irritation
Soap allergy
Perfume allergy
Fungal infection
Hormone replacement therapy
Paget's disease
Breast cancer
Eczema
Nipple rash

I hope you get it figured out - it sounds horrible

Love the name, btw

Hey your not alone, I to have an ichy nipple and it's on my left nipple, I claw it and it gets very sore because I've scratched it so much. I am fed up with it, I've only had this problem a few months now. I'm going to see my doctor next week if I can find the time. I will let you know what the tock tells me and if any treatment works.