Need advice

My period is irregular. I have a 29 / 30 / 31 day cycle. And usually my period is constant. 6 days long. It has always been like that. This month so far it has been for 3 days (medium to heavy flow) and today nothing. What???? As I am lieing on the couch I have a pain on my lower left side of my abdomen. Can someone give me some insight?? What do you think??