The only way to diagnose a pregnancy is with a positive pregnancy test. Everything else is pure speculation.
The BBT (Basal Body Temperature) curve is used to look retrospectively at the day you ovulated. Typically, the temperature rises within 1-2 days after ovulation and stays elevated until the menstrual period arrives. This is called a 'biphasic curve.' A 'triphasic curve' is a curve where the temperature rises again, often within 7-10 days after ovulation. There is no scientific proof that a triphasic curve indicates reliably enough that there is implantation and that you are pregnant.
A reliable way to diagnose a pregnancy is when:
Before those 15 days after ovulation it's close to impossible to know for sure whether you are pregnant or not.
If the BBT is elevated for more than 15+ days without a period, there is good probability that you are pregnant. And a positive pregnancy test at that time will usually confirm the pregnancy. Unfortunately, before those 14-15 days are over, there is just no consistent enough way to diagnose from the height of the temperature or from a triphasic curve whether you have become pregnant or not.