I Was Supposed To Get My Period The First Week

I was supposed to get my period the first week of December (1-7) but I didn't and then I had sex the day after.(I didn't have sex anytime prior that would make me miss my period) and the through out December I experienced the symptoms of my period but I still never got it. It is now January 1st and idk if I should take a pregnancy test or to wait another week to see if I get my period. Please help...