If it's primarily external then you should get checked for Lichen Sclerosis - it's an auto-immune skin condition that affects the vulva, more common in menopausal women. Left untreated it can lead to tearing and scarring of the skin which can build up and cause narrowing of the vaginal opening, plus a slightly higher chance of vulval cancer. It needs to be diagnosed by biopsy, but can be treated successfully with steroid cream.