How long does cramping post IUD implant last?

I got my Mirena IUD put in on Tuesday (4 days ago) and I'm still having some uncomfortable cramping on and off throughout the day. I'm wondering how long this lasts for?

Also- my period used to be like clock work and should have started 3 days after the implant was placed and hasn't come yet. Could this be part of the reason for cramping? My period cramping is normally horrible to the point of vomiting or not getting out of bed