Here's my experience with an IUD:
Painful insertion (Ibuprofen helped but the cramping was like childbirth).
Very, very painful cramping, sometimes seemingly unrelated to a period.
Heavy and more frequent periods.
However, knowing that I don't have hormones in my body and have a regular cycle (after being on the shot for many years) have made my husband and I more comfortable that when we do decide to start our family, we will be able to conceive.