Hi Doctor......I Am Having Irregular Menstrual Cycles....from So Many Years.now

Hi doctor......I am having irregular menstrual cycles....from so many years.now this cycle I got for three months and I am having prolonged cycle of more than 12days.so I have used tab.regestrone 5mg(once daily) for three days and bleeding was controlled but 4-5days after I am again getting bleeding now . So what should I do? Please help me....this is my exams time,so I am worrying