AF 4dpo?! What is happening?

Caitlin

So I have not had my cycle back since having my daughter 10 month ago. I’ve taken ovulation tests on and off during that time and never got a positive. This past Saturday I finally got a positive and was so excited to finally be able to ttc. But then on Thursday my period started 🤔 I have always had very normal cycle and after my first it went back to normal at 9 months PP. Has anyone experienced this? Or have any insight on why my luteal phase would be so short?