Frustrated and confused!

Hi ladies! I'm 26...27 in a few days, and my husband and I are on cycle 4 TTC baby #1! As of today, I'm 6 days late for AF! My bbt has been elevated for 20 days since ovulation as of today, which should indicate that I'm pregnant. However, my tests aren't reflecting that! So naturally, I'm super frustrated at this point. I've read that some women don't get positive tests until later, so I'm hoping I'm one of them! Any ladies here have experience with getting super late BFPs, or know someone who has?? Or, know of any other explanation for such prolonged high bbt without being pregnant? If I don't get AF by Wednesday I'm going to try to get bloodwork done to get some answers.