What Causes Spotting With Abdominal Cramps?

Hi, i got my implanon removed on 5 January 2011, i have been actively trying to conceive. I had spot bleeding with abdominal cramping on 20 February which just lasted a few hours and no more bleeding. I done a pregnancy test today 22 February it wasnt an early morning one and it came back negative. What does the spot bleeding mean?