What Causes Blue Round Bruise In Vagina?

hello i have a a blue round bruise (skin inside the bruise is white as is the outside. it is a perfect circle) on the right upper area of my virgina it is not painful but i had a pimple sort of thing there around 1 year ago. i am 24 and wieght 83Kg and have 4 children and have not had a pa smear for around 6 years. i am wondering if it is scarring or something more worrying. thank you