IUD at 16?

I have really long and heavy periods normally 30+ days with very bad cramps and I’ve been on the pill and the implant but they haven’t worked so my doctor suggested to try an IUD but I’m only 16 and when I told my mum she was shocked they want me to have it as I’m young and haven’t given birth or anything so I was wondering if it’s going to be bad to have because of my age? Also due to migraines I can only have progesterone only birth control