If your cycle is truly very irregular, then it is best to see a doctor and find out if there is any way that can help you to increase your chance. Meanwhile, I'd suggest you start taking your basal body temperature every morning before you get out of bed. It will help you to understand your own cycle. Usually after a few months, you should know your cycle pretty well. Other than that, try to observe your cervical fluid every day. In normal situation, the cervical fluid will increase and like "egg white" (very strechy and slippery) around ovulation and if you have sex when your cervical fluid is at the best condition until you see your basal body temperature rises (which means you have ovulated) then the chance will be much higher. The Clear Plan can also help you to pin-point when is the best time to have sex. Once you see the positive result, you should keep on trying for at least 36 hrs or until your basal body temperature rises.
Another good thing about taking your basal body temperature is that you can know whether there is any potential problem that decrease your chance. For example if your period starts very soon after ovulation (shorter than 10 days) then it may indicate that you have too short luteal phase. Or if your high temperatures do not remain above the coverline following ovulation, it could be an indication of low progesterone levels. All these information can help the doctor to treat you easier.
Most importantly, you should relax because stress can delay our ovulation. Usually ovulation happens 14 to 16 days before our next period so if you know your cycle better, it will be easier for you to know when to have sex.
Anyway, hope to hear good news from you soon. Take care.
小傻妹, I'm very sorry for your lost two years ago. I also just miscarried last month but I am doing a lot better now. I will start trying again soon. Hope you are doing well and wish you all the best!