threatened miscarriage?

Hi all,

Would it be possible for a threatened miscarriage to occur around 12 days after sex? I assumed it takes around 6 days for implantation; meaning when I was 1 week pregnant. I experienced vaginal bleeding (dont remember if there were clots or tissue in the discharge) which was similar to my period, i.e. with abdominal cramps and similar flow, but it only lasted for around 4 days. (my usually period lasts for around 5 days). I havent taken a pregnancy test yet and am afraid to.

Thanks for your time!