One day period?

I had unprotected sex and am not on birth control. Not a smart decision on my part- we were drunk and pulled out. This was on June 29th. On Friday July 5th, I thought I started my period because of quick heavy blood flow. It’s now Sunday and have only slightly spotted once or twice since the Friday. Haven’t even had light blood flow, just spotting. This is all happening a week before I should’ve even started my period. Of course I’m worried about pregnancy but am hoping there’s another cause. But this does sound like implantation bleeding. Please help.