Luteal phase question

I’ve had a short luteal phase (around 8-9 days) for the last 3-4 months and last month it was 9 days.

This month I’m 12 DPO and still no period. Is it strange that it’s gotten 3 days longer in a month? I had the same problem when I weaned my first daughter but I needed progesterone to lengthen my cycles and every month I would gain a day. It never jumped like this.

Could this month be a fluke or could I just be pregnant? Took a test this morning and it was negative. Sorry for the rambling post. Thanks for you insight!