Iud/Missed period

I had a baby back in March. And at my 6 month postpartum appointment I had a iud put in. Got my first period July 9th. I'm now 11 days late took a pregnancy test 5 days ago but was negative. Should I get another period. my doctor told me my period would stop after a year. Now I'm scared because I haven't gotten my period. Has anyone had this happen to them.