8 dpo

So I've had 3 positive hcg and all my opk have been positive so I went to the doctors today and there's came up neg if I am pregnant I would only be about 3 1/2 when I asked the doctor what would cause a false postive she said there test may not be as sensitive I did take a digital that came up neg as well so is it to early I'm supposed to go back in a week for another test mind you they refuse to let me take a blood test. Has anyone else had anything similar.