I missed my period this month !!!

My boyfriend and I have been having sex for about two months and we have always been careful. The condom has broke on us once but I took a Plan B pill the day after. We haven't had any incidents after that and have had protected sex every single time. However I am 6 days late. I took a pregnancy test on the 4th day that I was late and it was negative; however, I still haven't had my period. I'm worried that I may be pregnant.