What Causes Blue Mark Below And Left Of Belly Button?

I have a small blue mark that has appeared about 2 inches below and left of the belly button. It appeared months ago and looks like a varicose vein under the skin .The doctor didn t know what it was but said if it began to form an irregular pattern to come back to her. I have had an ache below it in the pelvic area for some time but it may not be related as the GP thinks it is the result of having fibroids. I am 62 years old and am still concerned as to what the blue mark could be . It isn t a bruise. Thankyou.