Have you had...a Black Thing (TMI warning)

So, my hubby and I had our first cycle TTC, sex everyday, and some signs of pregnancy. Blood test and HPT says negative and we're okay with that. Question- my period was a day late, then the next day there was a small black (blood?) mass when I wiped then nothing...my period stared as normal the next day! 
We suspect this very well could have been an egg that didn't quite take?? 
Some feedback or comments welcome.