Not sure what dpo I am on

Candice • 🎀10/2/2000 🎮 2/12/2003 🎀 due 7/23/2019

So, I had my cycle 8/5-8/7. I purchased the clearblue Bluetooth ovulation kit and i had high fertility 8/13 and peak fertility 8/14 and 15. I had sharp right side abdominal pain I believe the 14th. How do o know what day I actually ovulated on! I took a test yesterday and it was a BFN. I’m so confused with all of this. My first two kids 18&15 were surprises so I didn’t go through the ttc phase. Any guidance would be appreciated