Wheres my period?? 15 days let 2 negative pregnancy test?

I suggest calling your doctor. I dont even know what a coil is, so i dont know what to say about that. But if your 15 days late, and your getting negative pregnancy tests, then either your not pregnant, you are pregnant and the test is just not working, or your pregnant but your hormone levels are low, or even possible that you were pregnant but not anymore, if you understand what im saying. Just make a doctors appointment, and they will take care of you!