What Causes Delayed Periods After An Abortion?

Hi doctor i was confirmed one month pregnent as it was three month we got married did not want to consive so took a decision to terminate with doctors suggession and aslo was cleared... now i have not yet got my periods hence my doctor suggested me to take sandoz regestrone 5mg twice a day ... 3days , i have missed to take second day morning will this cause any side effect for my future pregnancy.. pls advise