wishin I have irregular cycles and I have conceived twice. When ttc#1 my cycles were 34, 42, 53, 35 and then conceived DS on day 19 (so it would have been a 33 day cycle). I was in the process of having day 3 and day 21 bloods to investigate my irregular lengthening cycles but got my bfp before I got the results.
The second time I conceived was whilst breastfeeding. My previous cycles since getting my first period 6 months after childbirth were 3 months, 6 weeks, then 8 weeks and conceived sometime in week 8 the next cycle. Unfortunately that ended in an early mc. But it just shows that you can conceive when you're irregular.
I'm considering going back to the gynae to get my cycles checked out again as they've been 23 and 37 days since the mc and am now on day31 and think I could be on course for a 45 day cycle.
If you know you're ovulating then charting temps, cm and your cervical position may help to pinpoint ovulation. But in my (unprofessional) opinion I don't think a range of 31-38 days is that irregular, you could just aim to have sex every other day from day 12 till day 26, preferably till you are sure you've ovulated which you should be able to tell via those charting methods I mentioned.
Have you read Taking Charge of Your Fertility by Toni Weschler? I found it very interesting when ttc the first time. I'm going for the 'lots of regular sex throughout entire cycle' method at the moment, but keeping one eye on my cervix position so I know when to expect my period. I have always had a tendency to stop having sex when I 'think' I've ovulated and then realising when period comes that I've ovulated later than I thought. So bad timing has been main problem to date. And it sounds like you have the same problem.
Apologies if Ive told you what you already know, just wanted to let you know that I didn't think you were that irregular and that if you've been told you're ovulating then you have to believe you have just as good a chance as anyone at conceiving (provided you have sex at the right time)