Hi Reei,
Charting your temp cannot predict 100% the exact day you ovulate, it only tell you the trend that whether you have ovulation, especially for those women do not have regular peroid. I have a friend who has the POCS problem, when she has the positive line on the OPK, even after a few days, her temp still does not rise. she cannot really predict her ovulation by using the BBT.
I agree with Mayc, you should the following signs to predict your ovulation.
1) Past ovulation records
2) Cervical Mucus
3) OPKs
