Implantation bleeding? Am I pregnant?

I am wondering if these might be signs that I’m pregnant, and if it’s even possible? My husband and I had unprotected sex for the first time EVER (in 4 years of marriage) on Feb 4th. According to eve, my most fertile window was about 2/7 - 2/14 with ovulation day being 2/14 I guess?? I was supposed to start my period yesterday 2/27 according to eve app. I took an “early detection” digital ClearBlue pregnancy test on 2/23 which said Not Pregnant. Today, i felt like I started my period so I went to the bathroom and there’s just a very small amount of brown blood in the pad. Which is very unusual for me. I have heavy periods, and I usually fill multiple tampons/pads a day. Could this be implantation bleeding? Is it possible I could be pregnant when we had unprotected sex over 3 weeks ago? We’ve used condoms ever since then. Thanks!!