Pregnant? Been 48 days? BFN???

Hey! I'm 21 and married, my husband is 25. Last period was Nov 17th. We had sex on the 20th which was when I was SUPPOSE to start my period but didn't!!! I figured if we had sex that day I would have been fine and not have gotten pregnant because I was about to start my period. Now it's Jan 2nd and no period????? It's been 48 days since my last period! I've taken test and they are all negative. What's going on???????