Everyone ovulates differently and at different times. The only way to accuratley know when you are ovulating is to track your periods. If you are irregular with periods it is more difficult to know when you are ovulating.
BTS1022 is right, the only women who ovualte on or around exactly day 14 are those who have a 28 day cycle every month, but you don't neccessarily ovulate every single month either which of course isn't going to make you feel any better (sorry). Start keeping a diary of such as to when your cycles are and when you are feeling dry or wet 'down there' which can help you track when you are having EWCM (egg white cervical mucous) which is a fertile time during your cycle.
If your periods continue to be irregular you may want to try some birth control to straighten them out at least that is what happened with me - when I was young my periods were all over the place but after being on the pill (did not want to get pregnant until I was married) for some many years my cycle stayed at 28 days even after stopping them. Talk to your docotor they may have other suggestions as I don't know how long it would take to regulate them for you - if they are only a couple days off here and there you would probably be able to just start keeping track. I hope you get what you are hoping for! Good Luck.
Roke said it perfect! Your ovulation is not based on your last period, but instead your ovulation will determine your NEXT period. Health classes don't teach it properly but you'll find this information all over on fertility websites.
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