Reddish discharge after sex w IUD

Savannah • a mountainess
Hi all,
I've had my IUD in place (Mirena) since December of 2013
I have periodically noticed pain when having sex, like it'll stop me in my tracks. And I'll sometimes not have any pain at all.
After sex I typically have darker discharge (not quite spotting but reddish)... What's up with that? Could he be hitting the IUD with his penis? Or should I go get checked out?
I am worried that sex is compromising the safety of the IUD if it's knocking against it so we have been using a condom as well, I'm wondering if anyone else has experienced this?