Mirena IUD/Painful sex???

Hiya! I’m 23 years old, I’ve been on the Mirena IUD for four years now. I’ll just cut to the chase cause I think I’m overthinking things thanks to google. Sex with my ex wasn’t as painful as it is now with my current boyfriend. HOWEVER!! my current boyfriend is much larger and certain positions hurt to the point of shooting pain but it doesn’t last the whole time. I’m tiny compared to him so maybe that’s also why it’s more painful?? I’m also not one that uses condoms (i know i know save the lecture please it’s my body) I’m not worried about pregnancy as i’m pretty financially stable as well as my current boyfriend. Just wondering if anyone else has experienced this? The worst pain is when getting railed lmao. I’m making an appointment with my OB/GYN asap just to make sure everything’s good, in the meantime should I be worried or just bare through the pain?

Edit: And maybe my fingers are too small?? but I also can’t feel my IUD strings which I know is sometimes normal, I just get paranoid hearing horror stories of women getting pregnant with the IUD. thanks!!❤️