Positive Beta Vs Negative HPT at 19dp5t

I had BETA Results on Tuesday that was BFP but a very low Number at 10 But my Dr Said don't worry about the number, the most important is the embryo is already There in your uterus, and she decided to do Blood work every 2 days, Wednesday and Friday but Ill get the results on Monday, I decided to test Today and look, what I got A BFN I'm so confused 😕 why is this happening?? I DON'T KNOW WHAT THAT MEANS