What Causes Cramps After Inserting Nuvaring?

I an on nuvaring I took it out last month and i started two days     later normally i start 4 to 5 days later. Ive had cramping tge day i put it in til now. The ring went missing then 7 days later I had a light period an was cramping bad before it came bt it was only a day and a half an then it eas completly gone bit was still cramping..what does this mean? My peiods are normally 7 days