What Causes Lower Abdominal Cramps And Back Pain Post Insertion Of IUD?

I m 21 year old female and got an IUD in February. I ve never been pregnant. I was told to check for the strings every so often. I ve been having lower cramping in my pelvic area , some back pain and a something doesn t feel right feeling. It doesnt feel like period cramps. I had what I thought was my period July 21st but was just spotting. Not sure if that s from having the IUD for a little while periods are not as consistent as before the IUD. As I check the strings for my IUD one seems longer than the other then when I ve checked it before. I feel as if I almost can feel part of the IUD plastic, but not sure if that s actually it or the string. I had unprotected sex July 4th and that seems to be when this has started. I m wondering how urgent it is for me to go in. I ve made a Dr appointment but I am unable to get in until August 29th. Should I take a trip to urgent care or the emergency room or wait until my Dr appointment.