2nd month of a Week early period?

I’ve not changed my lifestyle at all but this is the second month my period has started a week early. Last month I ovulated on time but started my period 7 dpo and the same with this month. Anyone have experience or theory on this?????

I’ve been to 3 different doctors in the past 8 months for unknown fertility issues and have had late periods, but I’ve never been this early before. And “unknown fertility issues” as in everything is great and healthy. I just have miscarriages for unknown reasons and they haven’t sent me to a geneticist for embryonic testing since I’ve not been (knowingly) pregnant in 6 months.