I saw your post from last night with your "super stupid BOTB question."
When I was PG with DD #1, I received my BFP, 10 days post O. I was scheduled for my annual exam 2 days later, so it was at 12 days post O. While I was there, I asked if they would run a blood test and the doctor said no because HPT's were so accurate--she said she knew I was PG. Then she went further and said that she could tell by my cervix as well. I don't remember what she saw that made her say that, but I would almost swear it had something to do with the color. I think it deepens in color due to the early PG hormones.
Good luck--maybe you could see if they will run a blood test for you?