Luteal Phase Spotting

I have a wonderful obgyn who I have seen and who is not concerned about this. I have normal CD1 labs. I am just having a really, really hard time wrapping my head around this.

I have a 25 day cycle and ovulate around cd13. This gives me a 12 day luteal phase. However, I started seeing brown discharge when I use the restroom 8DPO and truly spotting brown on 10DPO.

I just don’t see how I can implant/ support a pregnancy if my body is already starting to bleed before the implantation window. Can someone offer any insight? Why doesn’t this concern her - it just doesn’t seem biologically possible to support a pregnancy when my body says “time to reset the cycle” before I would implant.

I have a follow-up with her in February but feel so desperate to understand.