I have been on the mirena for about 4 years now, an this has never happened to me before. Last month (August) I had 2 periods 1 in the begining of the month and the other in the end, this month(September) I haven't had any so far and the month is almost over. I'm worried that the birth control may be wearing off since it lasts 5 yrs, and that I could be pregnant while on it.