What Is Causing Severe Abdominal Cramps And Pain In Ribs 3 Days After My Miscarriage?

I have just had a miscarriage two days ago at 7 weeks gestation! Went to hospital on the day and seems i had past the baby a few hours before...had bad cramping on both sides of lower abdomen so had scans to check for eptopic, no signs however i did have a something left which was sitting in the cervix.
I decided to try let nature take it course and hope that it would pass on its own.
Today day three after the miscarriage, i had severe cramping to the point where i thought i was going to pass out. Now my ribs are aching, extremeley tender and can only shallow breathe. I cannot lie down only feels worse. Why? I have had two other babies naturally at full term and used no pain relief for them. Im very uncomfortable.