Women ovulate about 14 days BEFORE the start of their next period, but it can vary each month either plus or minus a few days. Some women have shorter or longer luteal phases (the time between ovulation and the next period), which can cause problems with conceiving. You can tell when you're going to ovulate by an increase in cervical discharge, that looks like an egg white, stretchy and clear. There are ovulation predictor kits that are sold in stores, they tell you on the instructions, but generally you will ovulate 24-48 hours after getting a positive on the ovulation predictor. You can also keep track of your basal body temperature. You take your temperature at the same time every morning after you wake up, before moving around, even before sitting up. Your basal body temperature is your temperature when your body is at rest and it can go up just by you sitting up. You usually have a rise of .04-.06 degrees the day after ovulation, so it tells you after you have already ovulate which won't help you much if you are trying to have a baby., but it is good to see how long your luteal phase is. Your temperature should stay higher through the luteal phase and start to drop before your period is due if you are not prengnant. You can also check your cervix position, it's normally high soft and open when you are about to ovulate. It takes a while to get used to the way your cervix feels so you would probably take a couple months to get used to it.
It doesn't matter if you have irregular periods, your luteal phase should be the same each month. The only problem you would have is that you do have irregular periods, so I suggest using ovulation predictors and taking your temperature so you will know right before and right after you ovulate. I used to take my temperature before I got pregnant because I had irregular periods and my temperature let me know right after I ovulated so I knew how long it would be until my period started.
It doesn't matter if you have irregular periods, your luteal phase should be the same each month. The only problem you would have is that you do have irregular periods, so I suggest using ovulation predictors and taking your temperature so you will know right before and right after you ovulate. I used to take my temperature before I got pregnant because I had irregular periods and my temperature let me know right after I ovulated so I knew how long it would be until my period started.
Hope that helps!