Am I Pregnant?

So my period was due on the 27th-28th of December and my boyfriend came inside of me on Christmas Day, and I am currently 4-5 days late to my period ( it is currently 1st of January) I took a pregnancy test a day before my period was due and it came up negative ( tested with urine from as soon as I woke up) , is it possible I am pregnant or is my body just playing games as sometimes my periods can be regular and then become irregular after a few months and if you think I am most likely pregnant when would be a good time to re test.

We are not actively trying for a baby, but if it happens we will be more then over joyed.