IUD and horrible pains. Doctor has no answers...

So it's been two months and every time I get my period I get awful pain I wouldn't even say like cramps the pain is so bad. I cannot go long without taking painkiller. I bleed randomly throughout the month. Every time I check the string it hurts like crazy for a couple of hours. I asked the doctor why this going on she checked to see if the size was okay and if it was placed okay everything is good she says! Trust she's good with 20 years of experience but has no answers to why j have this pains. Is anyone else like this??  Or have been and how long until the pain stopped or what did you do to make it stop?