I had sex with my Fiance' on the 28th of February while on my period. I continued to still have my period as scheduled the next follow month in March which started on 24th. Now in the current month of April I started to spot on the 9th after having sex. I keep very accurate records of when my period starts and it was suppose to start April 17th and it hasn't. My question is what could be the cause of the spotting and the lateness of my period?