What Causes Missed Period And Vaginal Spotting After Taking Primolut N?

I am 27 years old. I missed my periods for the month of feb but had spotting throughout. I then took
2 primolet n per day for 5 days. It's been 2 days since I stopped primolet n. I have not got my periods as yet. When should I start worrying and go to the gynaecologist? Does spotting indicate something wrong?