Help! Might be pregnant!

Okay so I've been on Mirena since May and every period I've had since has been really heavy and long and then all over a sudden stopped. I've also had all the pregnancy symptoms from my first pregnancy. I know almost no one gets pregnant on the IUD but do y'all think I might be? My aunt (who's a nurse) told me I won't test positive on a hpt even if I was cause of the IUD. I just wanna get someone else's opinion before I begin to freak out.