I'm confused could I be pregnant, or is it all in my head

I have had unprotected sex 3 times since November 20, I had been feeling a little weird thinking I could be pregnant.  My period was late it's usually consistent nd it came the last week of November falling in December it was very very light and lasted4 days.  But I had already had my period for November. So after having sexy the 2nd time , I took a pregnancy test which was negative! Did I take the test too early? Should I wait a while longer ? ​​