I have the same problem. I started TTC in December and went to see my OB/GYN in January for yearly check-up. He said that I should chart my BBT (like Heather5 said above) so that I know if and when I am ovulating. He was worried that I wasnt ovulating and charting would determine that. I have been charting ever since and now I have detected ovulation 2 times! I am 7 days post ovulation and I am hoping this one is the one.
Good luck and if you have any q's I would be glad to try to answer them!
If you have irregular periods, I think the best thing you can do is to start BBT charting to make sure you actually ovulate. If you do ovulate, I would just continue having unprotected sex about three times a week (or every other day) for now, as it can take a normal, healthy couple up to a year to get pregnant :-)
If you're still not pregnant in July, you could consider seeing a specialist who can run some tests for you and try to find out if there's anything wrong.
Good luck to you!