HELP!! LATE PERIOD

My period is late by 3 days now which NEVER happens. I am never ever late.

I started having today (3rd late day) the occasional brown spotting but very lightly, and cramps as I usually have when I’m on my period.

I’ve had a lot of sexual activity with my boyfriend during the last couple of weeks after my last period, but no penetration as I am a virgin. During that, our two genitals touched raw from time to time.

What does this mean? Is my period late because of hormones and that activity? Or what? i know I’m not pregnant but I want to know why I’m late

Thanks in advance.