Welcome to MDC!! You've definitely come to the right place for support and advice. This is the Fertility forum, but there are several subforums for Trying to Conceive and Infertility. I highly suggest you repost over in one of those or both to get more responses. I know there are at least 2 other women that frequent the TTC forum that are doing IUI's right now. You can find the links for the subforums at the top of this forum. In the TTC forum you'll also find lots of support threads for those in different places in their TTC journey like age based, waiting to O, in the 2ww, nursing and TTC, etc. Check them out and jump in!
But my number one piece of advice is to start charting immediately. OPK's work for some women, but are often very unreliable for others and sometimes randomly so. Some women never get positives, others get positives for days on end, and some get positives well after confirmed O. Plus there are the interpretation issues with the strips- trying to determine if the test line is truly darker than the control line. And with the straight +/- kind you could easily miss your peak day. With something as costly and time consuming as IUI's I would not rely solely on OPK's.
Charting your basal body temperature and cervical fluid will allow you to see what your typical pattern is. You mentioned that you tend to get EW CF but not a positive OPK. It's quite possible that you're missing O by a few days! Charting will show you when you're fertile, if/when you ovulate, how long your luteal phase is (it is generally agreed that you need at least 10 days to sustain a pregnancy), when to test, when to expect AF, if you're pregnant, and if there is anything else of concern happening with your cycle. If you need help getting going with charting, just post over in the TTC forum and I'm happy to help you out! Good luck!