What Causes Delay In Periods And Light Spotting?

Hi, I have had a Mirena implant for the past year and a half. A couple weeks ago, my husband and I realized it fell out. I started showing all the signs of pregnancy (I have two children already) and took a couple tests all of which were negative. My period is three days late, and today I've had some pink tinged mucus come out. I don't remember that ever happening before. Any ideas?