How can I get pregnant if I have irregular periods?

you can also go by your temperature, i believe a rise in your temperature can indicate ovulation (obviously you’re not ill and have a high temp due to that reason), you can also by kits that tell you when you are ovulating, but i’m digital thermometer will help.

A rise in body temperature.

Following ovulation, your temperature can increase by 0.4 to 1.0 degrees. You won’t feel the shift, but you can detect it by using a basal body temperature (BBT) thermometer. This temperature spike indicates that you’ve ovulated, because releasing an egg stimulates the production of the hormone progesterone, which raises body temperature.

You’re most fertile in the two or three days before your temperature hits its high point. A few experts think you may have an additional 12- to 24-hour window of fertility after you first notice the temperature creep up, but most say that at that point, it’s too late to make a baby.

“It can take one to two days after ovulation for progesterone to build up enough to raise your body temperature. But since the egg can only survive for about 24 hours, at that point, it’s too late for fertilization,” says Tracy Telles, an ob-gyn at the Permanente Medical Group in Walnut Creek, California. That’s why experts recommend that you chart your temperature by taking it each morning for a few months to detect a pattern and pinpoint your likely ovulatory date. Then you can plan to have sex during the two to three days preceding the day your temperature normally rises.

Good luck.