short period?

[bushisgonein08.livejournal.com]

so i started my period on tuesday..and i had very very mild cramping..that was it..
wednesday was fairly normal..kinda light.
thursday i was down to spotting..
and friday i was completely off my period
so i really had a 3 day period..
im not on any birth control
and i had no PMS symptoms before i started
and after tuesday, i had absolutely no cramps or anything.
it was just a tremendously short period..
i thought maybe i was pregnant because i know people who had periods their first month, but very short ones..
so i took a test this morning
and it came up negative..
so what could be the cause of my really short period?

my periods usually go as follows:
first-second day light
third-fourth-very heavy
fifth-light
sixth-off

which is why this 3 day thing has kinda thrown me off..would this effect my ovulation as well? because me and my fiance are TTC and i dont want to have to track my ovulation or whatever..