Can’t find IUD strings and cramping

I’ve had my IUD for about four years now and haven’t had many issues. I still get periods but they are usually just light spotting with no pain until this month. I’ve been heavily bleeding for about two weeks now with some pretty severe cramping. I always check my strings once a month. I checked last night and I can’t feel them. I checked again this morning and still can’t feel them. I’m still having bad cramps. I called my doctor this morning and she can’t get me in until the 29th. As the day has gone on, the cramps have only gotten worse. I plan on calling again Monday to see if there is any way she can get me in sooner, but wanted to see if this is something ER worthy or not. I’d hate to go if this isn’t an emergency, but I’m beginning to get worried. Like I said, my periods are usually very light and painless, and they typically last 4-5 days at most. I typically have a pretty high pain tolerance, and these cramps are so bad that it’s making me nauseous. I truly don’t know if I can wait until the 29th.