Hi ! You are not feeling your strings because may be the IUD has shifted its position a little higher. Many females are intolerant to IUDs and they have pain/cramping pain in their abdomen. The dizzy spells may not be related to the IUD. If the symptoms and discomfort persist, it is suggested that you get yourself reviewed by your gynaecologist who may examine you clinically and get some tests done to exclude a pelvic inflammatory condition due to the IUD being a foreign body to the uterus
. She may even consider changing the IUD or suggesting you for some alternative means of contraception
WIshing you an early recovery.