anybody heard of this ?

I was due for af yesterday, and literally got nothing until early this morning at around 2 am I went to the bathroom and I have brownish pink spotting, it's been like that all day, not even going onto a pad...I had intercourse a couple hours ago and it didn't even make it heavier it's still light pink and basically non exsistent... my ovulation days were supppose to be Jan 3-7 and af was due on 18th...I took a test yesterday and it was negative... also I have no cramps, and typically when I start it gets heavier as the day goes with mild cramps...any insight?