Help please! So confused!!!

Ok so last month on the 08th of December I took a pregnancy test that came back positive. I continued taking a pregnancy test (at different times of day and different pregnancy tests) for about a week after that. 6 of them came back positive until after about a week and then 2 of them came back negative so I made a Doctors appointment for bloods. My bloods were taken on the 19th of December but the results came back “not pregnant”. I had no bleeding at all. However, my period is now 3 days late and there is absolutely no sign of her. So why did I get 6 positives, then 2 negative hpt and then a negative BT but with no bleed at all, even now? Has anyone else experienced this and got an answer? Thanks