Well to start with I'm not sure exactly what a iud is. So that may or may not play a factor in trying to conceive. But here are two suggestions which you may or may not like.
1)Have more sex. Since you have an irregular period, I'm assuming, that you are not sure when you ovulate. But if you can figure that out then have even more sex around that time. By having more intercourse you are more likely to conceive.
2)May want to try in vitro fertilization. Which is basically they take an some eggs and some sperm and fertilize the eggs in the lab and then replace them into the womb and hope for attachment to the uterus wall.
But if the second option is something you don't want to do and you're still having issues with option 1. You may want to check how active his semen is and other things such as if the uterus and vaginal juices are too acidic/basic for the sperm to live in.