How do I know when I ovulate without taking a test.

Jacqueline • Mummy to twin boys after 2years ttc 💙💙
Hi there me and my fiancé have been tryin for a baby for the last 10+months and nothings happend. My periods have been coming every 3/3 n half weeks so tryin to figure out when I ovulate isn't making sense. I promised my other half I wouldn't go down the ovulation test route but it's gettin the better off me. Anyone know hat I can do x