3 missed periods, but a negative pregnancy test. What is wrong?

Posted by so_grad

I went off nuvaring on Aug 2nd (meaning I had just finished my cycle and I was suppose to begin a new one that day).  That evening I had sex and we thought the condom broke so I took the plan b later the next day.  I missed my period in september, so I took a pregnancy test sept 20th which as negative, as was one a week later.  I still have not had my period.  Am I pregnant?  What is wrong?