I have had an IUD for over five years. Itching symptoms I have had since I can remember, but became severe this time last year. It interfered with our marital sex life, I couldn't wear jeans, sitting down was a nightmare, and at night the itch drove me nuts. My doctor diagnosed me with lichen scerolsis and prescribed a steroid oitment (clobetasol propionate .05%) which keeps the itching and pain at bay. She was able to diagnose me with a visual examination and said that the skin around women's private parts becomes extremely thin and looks like parchment. She also said if she had been unsure she could biopsy it.
There is not much out there on this condition, but please ask you gynecologist if this could be what you have. I strongly suspect it becomes more severe as one approaches or enters perimemopause or menopause.
I hope this helps you. It certainly was the diagnosis for my problem.