Had the mirena (levonorgestrel) IUD inserted last friday. This is day 4 of really bad cramps. How long does the cramping last. I tired of it, cause my period is over!

Unusual. Usually cramping is associated with iud insertion. Severe cramping after 4 days is unusual. Check with you doctor, make sure there is no perforation, of course this is uncommon.
IUD cramping. With severe cramping for 4 days after iud placed, you should have this checked out with an ultrasound to make sure the iud is in the correct position ; need to rule out perforation of the uterine wall.