What Causes Delayed Periods Post Intake Of Primolut N?

I have taken primolut n for 2 days at the beginning of my last cycle (end of Nov 2014) to delay it, but it was just lighter and when I stopped, the period was quite heavy. I have not had a period since, other the 2 days of spotting at the end of Dec 2014? Have I caused potential imbalance?