IUD & pain during sex

Alex
Hey! I got an IUD (the copper one) back in February and it was SUPER painful. Sometimes it hurts during sex and my bf can feel the string. I noticed that at the end of my cycle, we don't have any problems. Right after my period though, it's pretty painful (beginning of cycle). Could it be because my cervix is lower or something? Anyone else experiencing this kinda thing? ... Thanks!