Hi Dr. Purushottam welcomes you to HCM virtual clinic! Thanks for consulting at my virtual clinic. I have carefully gone through your case, and I think I have understood your concern. I will try to address your medical concerns and would suggest you the best of the available treatment options. Usually after mirena insertion ,within 3 weeks its medicinal action starts with fully, as a contraceptive device it works from day one. Whatever clot you might have passed can be due to uterine gland secretions and some minimal blood. And while passing out from cervix-mouth of womb , it must have caused you low back pain. I suggest you not to worry, if at all you have doubt you can get urine pregnancy test done. I hope my answer helps you. Thanks.