How can I be absolutely sure I am not pregnant?

The chances of you being pregnant with the Mirena is VERY SLIM. I work for an OB/GYN for 19 yeaars now, & have experience with the Mirena. It won't let you get pregnanct because it is a foreign body in your uterus, thus pregnancy won't implant. Do you drink alot of pop, coffee or tea or eat alot of chocolate?? These things are high in caffeine, and caffeine in excess will make your hurt, sometimes so badly it hurts to go without a bra. Also, the hormone in the Mirena can cause no periods, heavy periods, irregular periods and tenderness. If your pregnancy tests were definately negative, try to cut back on the caffeine, see if that helps the tenderness. Worrying & stress can also make your period late. Otherwise, try a Planned Parenthood or Health Department, if there's one near you, they can do a blood pregnancy test for very low cost or sometimes even free. A blood pregnancy test is 100% accurate. Hope this helps you out.