Why is my period late? It’s never late!

girl next door

I’ve had a normal 27 day cycle, period 7-8 days long while having the Paraguard iud for the past 1 year 1/2. Today marks 2 days late on my period, I had spotting on December 31st, and some harsh cramping but nothing came out of it. Negative pregnancy test 3 days ago. What’s going on?