Ummmm???

According to the app today is my highest chance of getting pregnant. I had sex last night and randomly today felt something as if I was bleeding. When I went to the bathroom I stained my underwear and realized i bled dark red blood. why is that.

UPDATE: this is an hour in between the original post now it looks like this. And I've been cramping non stop since Saturday. Spotting off and off since Thursday. And bled a light pink Sunday night.