What is happening?

I'm 15 DPO, I had some spotting on Monday and Tuesday, got a very faint BFP on Thursday from First Reponse (using FMU), a very faint line on the cheap strips from amazon yesterday, Friday (taken in the afternoon). But today (Saturday), my bbt suddenly dropped, I took another First Response using FMU and if there's a line at all, it's vvvvvvvfl. AF was due on Wednesday. Any idea what is happening? I miscarried in January and it finally seemed like this month was the real deal 😩

Thursday's test:

This mornings test: