Livre d'Or

That's not medically plausible. The second half of your cycle (the luteal phase) is the consistent bit. Even in the most variable cycles, the luteal phase rarely varies more than a day or two and is almost always 13 or 14 days. Anything other would be some kind of medical issue.

There's a great book called the fifth vital sign.

And I don't take my temperature at the same time each morning. I have a view of how it changes according to whether I get up earlier or later than normal and adjust my interpretation of the reading. (it's always low or high anyway, just less consistently low or high)