I Have Quite A Few Blood Blisters On My Labia

I have quite a few blood blisters on my labia majora and was wondering what causes these. I am very self conscious about them even though my husband doesnt seem to mind them. I saw my ob/gyn about them but she seemed to think they were normal. This morning while shaving, I cut one and it bled for quite a while. What are these, what causes them and will they ever go away. Should I be concerned?