Cramps after sex then bleeding?

I am 12DPO today. Negative pregnancy test this morning. AF is due Wednesday, this is Sunday.

Had sex with my husband last night and started cramping after. That’s never happened before so I got excited thinking maybe early pregnancy symptom as I would be 4 weeks pregnant today.

Cramped all this morning. Just went to the bathroom and had a little red blood on the toilet paper.

I have read that implantation bleeding would not be red, it would be light pink or dark. I have never started AF this early though. I’m like clockwork every month give or take a day that the app predicts I’ll start. I’m never 3-4 days early.

I guess I’m still hoping there’s a chance I could be pregnant. That was the first i have seen of the blood so not sure how long it’ll last. Anyone had this happen and then been pregnant?