Ursula, I think its way to early to get stressed out about infertility. And if your cycles are irregular, those fertility monitors are practically useless because you need to have an approximate idea of when you expect to ovulate in order to use them. If you want to put your mind to rest, I would recommend charting your temps. It may sound like a lot of trouble, but, honestly, once you start doing it, it's no big deal at all. Just pop the thermometer in your mouth for a couple of minutes when the alarm goes off in the morning and record the temperature. And the benefit is that you can often tell from your temps when you are pg several days before your period is due. With DD #2, I knew I was pg before I even took the pregnancy test - 10 days after conception. Good Luck to you! Oh, and BTW, even if you are not ovulating, lack of ovulation is often very easy to correct without having to jump thru hoops.
Kim