Could I be pregnant?

My last period was between November 11th-November 15th. In the app, I was supposed to have my period on December 14th, but it never came. I am usually at maximum a week late on my period. My husband and I had unprotected sex the day the app predicted I would ovulate. However, when I took a pregnancy test about a week ago, it was negative. I also had unprotected sex a week after my predicted period. Since Sunday, I have been really nauseous after eating and extremely tired at work. Could I have ovulated late this cycle, causing my period to be late? Could I still be pregnant?