Thanks for consulting us.
I have few suggestions for you.
I hope you feel your coil's thread each month after your periods & it is still inside you.
If the coil is still inside you & you are not having periods you must see your doctor even if home pregnancy
test is negative.
I recommend you to have a blood pregnancy test & a trans-vaginal sonogram to exclude an ectopic pregnancy, which could be a possibility in your case.
If you have taken some hormonal
medicines to decrease your menstrual flow this may be the cause of your delayed period.
Your Gynecologist can guide you for further work up & treatment to regulate your periods.
Wish you good health