No period since IUD insertion

I got my first IUD, Liletta, on September 24th and I have not had my period since. Also, as my doctor advised I waited a week before I had sex. When it was inserted my period was already 2 days late. I have an incredibly irregular cycle, it has never been on time and has always started 1-8 days after it should. Before insertion they had done a pregnancy test and nothing came up so that was not a worry of mine. After it got inserted I had very minimal cramping, and I had light bleeding but nothing like what my heavy periods usually were. I’ve had the brownish blood / discharge ever since, and occasionally have found more fresh blood, but only spots here and there. I have also experienced light cramps for a few hours during those fresher blood times.

That fact that I have not had a proper period is a bit concerning to me and I was curious if this is something that has happened to anyone else or if I should be concerned.