IUD questions: Option Mirena

Okay I just got this put in 2 months ago. I noticed that recently my string has been getting smaller. And I haven't had my period for over twenty eight day, so that is wierd for me. Is this a good thing or a bad thing, should I see my doctor. Because I was told the Iud shouldn't move but my string is smaller. I was also told that my period would still happen regularly but may be lighter. Can anyone advise me somehow