So I am on CD 25 and AF usually comes around CD 26 or 27. I believe I O'd on CD 17. In the last week when my husband and I have had sex, when I go to the bathroom afterward there is a slight brownish hue to the liquid that comes out. But I don't have any other spotting. I only notice it directly after sex. Is this maybe implantation bleeding? Or just a sign that AF is coming?