IUD/ negative preg test

Okay so I went for the Mirena birth control, and had a pregnancy test done. My test came up negative but I haven't had a period in over a month but had light spotting just on the 23rd of last month. I was then told that I had to be on my period to get the birth control I wanted. The same place told my best friend she wasn't pregnant 3 times whe she was really pregnant, and she was able to get her Mirena IUD without being on her period. Was I misinformed or was she?