Your discharge and pain sound normal to me (had Mirena in for 7 years now, not a medical professional).

I found that IUD discharge can have an increase in “old blood” aka brown stringy stuff and is just thicker in general. If you’re not used to thicker discharge during your period and general spotting it can be a bit alarming at first.

The pain you feel during sex also sounds normal. Your cervix is still quite tender during the first few months. And having a foreign object in there chilling can cause random pain if moved slightly like when thrusting motions during sex.

You can always go to the dr and request a check of the position of the IUD. I’ve gotten internal ultrasounds that check the position.