Day after iui, having moderate to severe cramps and lower back pain, was told to have sex today, it was very painful. normal or should i call dr?

Call the doctor: Ovulation can cause cramping, but there is a small chance of infection from inseminations (iui). A fertility clinic performing an IUI preparation should see signs of infection such as white blood cells in the sperm, before proceeding to 'wash' the sperm (prepare it for iui). If there is an obvious infection they would tell you not to do an IUI this month, but you can still have timed intercourse.