So I need some advice!!

I had unprotected sex Aug.15 but literally for a few seconds then we used a condom. So right after I took a Plan B just to be safe because I read sometimes precum can have sperm. However I was ovulating that day and I also read that Plan B doesn’t work when you are ovulating. However I got what I think is my period Aug. 30, but it’s super light and that’s not normal for me I have a heavier flow, I finished what I think is my period yesterday. However I had no extreme period cramping like I normally do. The other days I was filling a tampon like one or two days but the rest were very light. The color has ranged from dark red to a lighter red some pink and now to brown and I’ve taken two at home pregnancy tests one on Aug 30 and one on Sep 2 and both came back negative. Am I stressing or could this be implantation bleeding ?