Hi. I Have A Question Regarding The Birth Control MIrena

Hi. I have a question regarding the birth control MIrena and discharge. I've had the iud for about a month that. I started my period two days ago and today I passed a tissue looking discharge. It was about two inches long and about an inch thick and was grayish in color. Is this normal? What could it be? This is my third time getting this form of birth control and I've never had this happen before.