I rarely have a period, but ovulate like clockwork. I used to use sympto thermic charting as birth control, and I would have a spike on the 19th day of every month and sometimes again on the 24th day. After watching this for almost 3 years, I was able to figure out that I have a 34 days cycle, ovulate twice a cycle sometimes, even without having a "period." I was also able to figure out that when my temperature makes that steep drop (progesterone levels dropping...I believe) I'm my weakest in the gym. Like W6 said, I just took my basal temp every morning at the same time, before ever even rolling out of bed. It's interesting the things you can learn about yourself in terms of strength, water retention, moods, mental clarity, etc...all by seeing how they coincide with basal temp charting, over time.
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