IUD Mirena HELP!!!

So I've been with my boyfriend for 1 year & 8 months . We have been having sex for about 1 year now. The first few months we used a condom. I thought I was pregnant this past summer but I wasnt thank God , hence I'm on the IUD mirena since December 14, 2015 so it's about 10 months I've been on it now & the doctor told me it's very hard to get pregnant while the IUD is installed in me (5years) . SO my question is, if he continues to ejaculate in me while I'm on iud mirena do u think I will get pregnant? I am 20 & want to wait until I'm about 28 . Pushing 30 lol.