Short period

I got my first period in 4th grade, since then my period had always lasted five days. I just got my period on Wednesday and it was gone my Friday night. I had no blood when I woke up Saturday morning, and No blood all day Saturday. Then Saturday night my boyfriend and I had sex and there was a little tiny bit of blood. Now today (Sunday) i have just kinda been spotting today. Like hardly at all though. So what could make my period only last for three days ? Should I be concerned? Im 23 years old, and fairly healthy.