I have had a messed up period pretty much since i started when i was 12. Four months ago i started dating my boyfriend and i was still a virgin and we werent sexually active. my periods were on time all four months. it is now approaching the fifth month and we just recently like starting having sex and then starting having it alot like one or two times a day. we always have used protection and are always safe. but this month i am now 6 day late for my period and i have taken 3 pregnancy test and all 3 have come back negative so i know im not pregnant. i have been having pms symptoms like headache and irrtatibility, a few cramps, etc. But i guess my question is, could my period be late because i just started having sex or could there be another reason?