Need help

So I have the IUD paragard and my partner has finished inside me both during and after my period what’s the chances of getting pregnant? I hear all these stories of women who get pregnant with this birth control so I’m freaking out. I went back for my 1 month check in and my obgyn stated it’s in place and I took well to it I check my strings and I can feel them they curled up a bit which is normal correct?

If pregnancy is so common then why is IUD compared to sterilization, so why do so many women get pregnant?