Bleeding 17 days early

Shatana
My cycle was just on and when it went off we had intercourse a few times and then I wake up one morning (17 days before my cycle is due) and there's blood in my panties. Not a lot but enough to put on a pad to be sure. I wore the same pad all day and today is day two but the bleeding is lighter than day one. What in the world could this be?