Idk what's going on with my body😐

Deah

The last time I had my period was Nov 19-23, 2017. I was supposed to get my period Dec 20, 2017 and here it is the last day of the year and still no period. I took a test two days ago and I could've sworn it was negative but then again there was a faint line there. But I don't know. What should I do?