What Causes Lighter Periods After Taking Primolut N?

I took primoult N tablet for 5 days, daily one . 2 days after stopping the tablet, I got period, but the bleeding was for half a day. Then there is no sign of bleeding. I am not sure if it is side affect of the drug. This is the 1st time I took this tablet. I may need to take it for next month for one or two days. Please suggest me what to do?