It could also be related to how your cervix changes over your cycle, but that baffles me because surely gynecologists would know that and try to time things correctly if it made things easier for women.
Do they time it based on your cycle at all?
Close to ovulation, your cervix goes really soft and opens up, close to your period it changes position, goes really firm and closes.
I haven't gotten an IUD so I have no personal experience with the process, but I imagine that trying to put an object through the cervix into the uterus would be best done at ovulation when your cervix is open. And probably extremely difficult and painful to try to do when your cervix is shut tight.
Whatever is there before baby will be made a thousand fold. Children are amplifiers.
If you and your partner already have a culture of flexibility and support and caring for each other you will be fine. It will still be work and there will still be tough times, but you'll be able to get through. You'll probably come out closer than you thought possible.
If either of you have bubbling resentments or distrust, or very rigid ideas about who should be doing what and when, the difficulties may be insurmountable.