Is this normal?

Lupe
I have had the Mirena for about four years now going on five. I recently started getting really bad cramps and weight gain. I also feel sick a lot. I asked my boyfriend because o couldn't find the strings or even feel it and don't recall it ever falling out. He said that he stopped feeling them a few months into our relationship... I also went to the doctor and she couldn't find them so I am questioning her as well. What do you girls think I should do? Also what is the removal surgery like if they can't find the strings?