How do i know ovualtion time?

im very irregular... af came sept 14th - sept 21st very heavy flo, in oct i had af but it was very irregular it came on oct 12th - oct 16th i wore a panty liner because it was so light, the first day of oct 12th we had , well i had light sore aches and then oct 25th and oct 31st we had ... well today is nov 5th and im back to having light spotting i wipe myself and see light blood now it has went away for good. how do i know when i ovaulate, are there chances of pregnancy? im ttc for almost 3months