each time i menstruate, i have little blood flow for one day only. what can be my problem

Well, you should talk to your gynecologist about this since light and short period may indicate a pregnancy, hormonal upset or may be a symptom of polycystic ovary syndrome. It may also be an indication of impending menopause. Stress from work or relationships may cause the bleeding to become more severe or stop sooner than normal. For some women, increased exercise may lead to a shorter menstruation cycle. I hope this helps.