Is it possible that I had late implantation and could still be pregnant?

So here's my timeline...

28 day cycle, Period due today. 

Last period was on 7/5. Unprotected sex on 7/16. Spotting began late on 7/27, which is not normal for me, and lasted through 7/30. Late 7/31 I had more actual bleeding that seemed like it could be the start of my period which was due today 8/1. Today the bleeding is about the same as last night, not nearly as heavy as usual. I took a pregnancy test yesterday afternoon which was negative. Is it possible that I had late implantation and could still be pregnant even thought my period still seems to have come on time? 

Not sure if it matters but I had a miscarriage last year in October at 7 weeks.

Please let me know! Thanks!