Yikes, this is a toughie. There really is no way to hide that and no excuse that would make any sense. I'm afraid your only option is to tell her. Being a gyn, she can't really do anything about it (as far as telling others); my guess is that she will be concerned about your mental health and suggest you see a therapist. Hopefully it won't be too awkward-who knows? She may be understanding! You'd be surprised...