My last period was on November 23. We BD 3 times around my ovulation. Yesterday I had some spotting too light for a pad or a tampon and it had stopped by this morning. My period is due on December 18. Does this sound like implant bleeding or a strange period? I took a pregnancy test yesterday morning and got a BFN.

It could be, but implantation bleeding is actually rare compared to what you might have heard.

Its also likely that you took a pregnancy test too early... it might be hard, but wait till you're at least 1 week late before you test again. :)