How do you know your ovulation days?

Difficult to say. If your cycles are irregular, it is difficult to predict ovulation. We can retrospectively tell when ovulation occurred by counting back from your menses. Your menses will always start 14 days after ovulation. It is the 1st half of the cycle that varies. Of course if you are irregular, you may not be ovulating each month. See your gyn for an evaluation and treatment. Best of luck!