Why is the flow of my period different some months?

The output: of hormones during the menstrual cycle is not exactly the same from cycle to cycle in many , in fact most women. This also varies with age. It is this hormonal effect on the lining of the uterus (womb) that determines the "thickness" of the lining and it is the "shedding" of this lining which determines menstrual flow. Hope this helps! Dr Z