possible pregnancy?

Okay so I started Depo back in sept of 2014 the last injection I had gotten was in dec of 2015 my ex and I broke up so I stopped getting the shot.  
My last period started December 24th and ended on the 28th but on January 4th I went to get back on depo. My boyfriend and I had unprotected sex on the 5th and he came inside of me. I'm 3 days late but I just took a pregnancy test and it says I'm not pregnant. Is there any possibility that I might be pregnant? Should I wait and take another test?