First timer

Hi ladies! I’ve never taken opk tests before. I’m on day 13 of my cycle, and wasn’t planning on using the test strips until next month, but now I’m kinda curious. We’ve been BD every day since day 8, and the app says I should be ovulating within the next few days. I’ve had some cramping yesterday and today so I’m thinking I’m close. It’s hard to know my cycle since I’ve been on birth control for 8+ years. This is my first time off of the pill. Any suggestions? Should I just start using the strips today?