IUD and no period since I got it

When I first got my IUD I was told I would still have my period for at least 6 months and it would slowly disappear until I didn't get it anymore, I got my IUD November 18 during my period, I still have not had a period, I've never been late before having my IUD, I had a little bit of very light brown discharge and a strange odor for a little bit during the week I should have had my period and absolutely NO period symptoms like I use to get so badly before then I'm back to normal. Is it normal for some girls to just never get it again right after the implant? I'm also asking because I've had unprotected sex since a few days after getting it in and since on, I went back on the 20th and she said that it looked good and in place