Still Getting Periods

6 months into the Mirena IUD and I’m still getting periods. They are regular, but late by 2-4 days the past 2 cycles. This cycle I’ve had heavier flows than any cycle since I started the IUD (I bled through my heavy period underwear yesterday which I’ve not done since getting the IUD)

Have any of you had this issue? Is this normal? Do some people’s periods just not stop with the IUD?