hi,
I too had really irregular periods and am now pregnant with no1.
I cannot recommend enough the book mentioned above 'Taking Control of your Fertility' by Toni Weschler'. It was suggested to me by my SiL and I found it really informative, well written & simple to follow. My husband and I had been randomly trying and i thought i had a fair idea of when to DTD, but we hadn't had any luck for almost 2 years.
Once you understand how to track your ovulation and look out for your fertile days its really easy to follow. i was able to track when stress at work or something similar had affected my ovulation, and i ovulated later in the month than i thought. I got pregnant on my 4th cycle using her methods - not that it works for everyone of course!
many of the points she raises are extremely interesting such as;
(and i'm only writing from memory here so may get some info wrong!);
-many couples having problems conceiving are asked to try for a year by their GP, but by charting using her methods, problems can be spotted within 6 months
-many couples are unnesscessarily put on clomid, and although it works in many cases, it can actually dry up the cervical mucus which is so important to conception (she actually suggests using egg white as a substitute!)
-so many things can affect your ovulation date such as stress at work/ anti biotics / travel etc etc
-it teaches you to look out for primary and secondary signs of fertility
as i say, its method may not work for everyone, but i certainly found that i felt more knowledgable about the whole process. And am so excited about the little one on the way!!
Good luck!!