HELP! ๐Ÿ™ˆ

The dilemma is, Iโ€™ve had a few positive pregnancy tests with faint lines. I am currently 12dpo and have been having cramps, nausea, insomnia, and so on. I went into the dr today to get a blood test and it came back negative! The doctor said โ€œfalse positives are not possible so if you donโ€™t get your period just come back in and retest.โ€ Plus she was definitely rude about the whole situation. So what Iโ€™m asking is, are false negative blood tests possible? Was it too early for them to detect the levels? What would you do if you were in this situation?! Please help โ˜บ๏ธ๐Ÿ™ˆ