If I do not have menstruation while using the IUD, can I be pregnant?

You did not write what IUD you use - each "spiral" has a certain length of contraceptive action, and after this time it should be replaced with a new one. For example, Mirena prevents pregnancy for 8 years after its inception, Kyleena for 5 years, Levosert says contraception for 6 years, and copper inserts (without hormones) also have different "lifespans". It is difficult for me to answer without further information whether there is a possibility that you are pregnant. In general, a properly functioning IUD provides high contraceptive protection, and the risk of pregnancy is negligible (but it exists). For example, information from the Levosert IUD documentation states that: "In the absence of menstrual bleeding for 6 weeks, a pregnancy test should be considered. If the result is negative, there is no need for another test unless there are other symptoms suggestive of pregnancy, e.g. nausea, fatigue and breast tenderness." A negative pregnancy test speaks for the lack of pregnancy at the moment, but ailments such as discharge from the nipple should prompt you to visit a gynecologist. The gynecologist may additionally perform an ultrasound examination that will check the IUD. You will also be able to answer a question related to protection against pregnancy. I enclose a link to information that may be of interest to you: https://www.gdziepolek.pl/artykuly/antykoncepcja-hormonalna