Copper IUD Missed Period

Hey Girls! 
I have had my copper IUD since April 2013 and I have had regular periods, the odd irregular spotting here and there but nothing to complain about. This month however I am currently 12 days late for my period, which is very unusual. I haven't had a weight change or stressful event and my diet hasn't changed.  I was wondering if anyone else has experienced this? Im starting to worry it may be something sinister. 
Thanks so much