What is going on with my cycle?

I was 15 days late on my period. I have the IUD but I have had it for 1year and 9months and my cycle has been dead on every time. On day 15 which was the 24th of this month and midday I went to the bathroom and when I wiped it looked like mucus with a streak of bright red blood in it. Since that when I wipe I only have had a very lite pink tint to the toilet paper and that's only a couple times a day. I am barely even spotting. What is going on? I took two pregnancy tests one when I was 10days late and the other the day I had the mucus with the streak of blood both were negative.