What causes IUD pain?

Hello mommy’s i had a question i got an IUD inserted last week i been having pain in my lower back sense the day the inserted so my question is
Is it normal to have pain like that? My mom’s friend said it because of my age just cuz something similar happened to her daughter were just a year apart
Am 18 by the way
And i also just had my baby a month ago by c-section could that be part of my back pain?

I talk to my doctor and he said he didn’t fin nothing wrong that the pain was going to be gone soon just to take 800mg of ibuprofen