Late Periods & a Copper IUD

I had a copper IUD fitted in late December 2019, before this I was on the pill which I stopped taking mid-December due to an interaction with a new medication.

The first few months were as expected with a copper IUD- regular periods (30-32 days), heavier bleeding and more cramping. But my last 2 cycles haven’t been as expected.

My period in April started on the 21st but I didn’t get my next period until 4th June (44 days). I took a pregnancy test which was negative and spoke to a Doctor who said this was normal (I found her to be a bit dismissive of my concerns). My period eventually came so I just forgot about the situation. That was until this month, where yet again my period is late.

Currently I’m 18 days late, and I’m not feeling any of the symptoms I usually get prior to a period- cramping, PMS, cravings ext. I’ve taken a pregnancy test to rule that out which again was negative. My coil still appears to be in place- I can feel the strings. I’ve booked into speak to a GP again at the end of the week, I just wondered if anyone had any thoughts on this and what could be behind it.