Why does it say?

So I have the Kyleena IUD since June, iv had regular periods and some occasional spotting but nothing over the dramatic.. BUT the last time I had a period or any kind of spotting has been 6 weeks.. so I went and looked at the leaflet that my doctor gave me and it said if you do not have a period for 6 weeks to take a pregnancy test.. this morning I threw up a little and have been feeling a bit nauseous all day.. has anyone had this problem or what would you recommend to do?