BBT charting help

Was wondering if anyone could help me out. So my doctor put me on Femara this month and I have been charting my bbt to see if I ovulated (because I usually don't.) According to this app I was scheduled to ovulate on August 23rd but according to my bbt chart my temperature rose from a 97 to 98.4 on August 24th. On August 25th it went back down to 97.8. And then on August 26th it was back up to 98.4. I was very excited when I saw a temperature rise because ain the last fee months of charting, it has usually just stayed about the same. But I took one ovulation test on the 23rd and the 25th and I took two on the 24th. I am new to this so I don't exactly know what I'm doing, so it would be great if anyone could tell me what may be going on. Thanks ladies.