What Causes Scanty Bleedng During Menstrual Period?

dr i am 41 year old having two kids. last four years i am facing less blood in during menstrul. but regular. every year go for pap smaer test and regular checkup also. but i wanted to why is like that. i am ITP also last four years but no medication only taking calcium and multi vitamin. some time i am sceard what to do . wait is 66kg height169.