IUD, Pelvic Cramps, No Missed Period

I’ve not gotten cramps when not on my period for 6 months (when I got the Mirena) but today I’ve had off and on pelvic cramps that hurt for a couple minutes and then go away for a few hours.

I’m about 10 days from my next period, have been having unprotected sex with my boyfriend about once a week, had a negative test on 9/11, and took a Plan B on 9/18 just as precaution.

What could be causing these random pelvic cramps?