Irregular cycle after copper coil removal

Nicola
Hi, I was just wondering if anyone else had experienced this?
I had my copper coil removed on the 15th December and my period should have started on the 24th, but it hasn't arrived yet. 
I've done 3 pregnancy tests and all have come back negative. 
I thought the copper coil meant that your fertility returned to 'normal' straight away and so I assumed my periods also would remain regular. 
I've had cramping for over a week, but no period has arrived with just seems strange...