My last period was January 21, 2012 and I had intercourse February 10th and the 13th and I missed my period in February, I then had a light period in March 09, 2012. My periods are irregular so i didn't pay too much mind to it but know that i think about it is it possible that i got pregnant in February and my light period was implantation bleeding? I wasn't spotting but it was light bleeding enough that at times i would need a pad and did pass blood clots. Also i took a pregnancy test 2-2.5 after i last had intercourse which was February 13th and the test came out negative, i did use my first morning urine to test. I already had two ultrasounds which have been measuring me 5 days ahead of my lmp. Is it because maybe i'm further along and possibly was pregnant when i had that really light period and the pregnancy test was perhaps a false negative ?