Which exactly is the last day of menstruation?

Asharteea
My first day has medium flow but it comes with nausea and fatigue. Second day is hell, it's heavy flow and cramps. Third day is light flow and no other symptoms. Forth, 5th and 6th day I'm just spotting. So is my periods length 3 days or 6 ... Im confused about how these things are calculated. I always say my period lasts 3 days...