What Causes Delayed Periods?

I am 42 years. I was diagnosed HT october 2010 and was treated with Nebicard SM 2.5. I missed my period that was due in first week of november. My BP is under control and I stopped tablets gradually. I consulted Gaenacologist this month and she suggested me Norgest tablet to start period but till today I have no period. What is the cause? is it due to BP tablet or Dothiapin 25 since last 8 years.