When do I ovulate? (See calendar)

I never tracked my periods prior to stopping birth control in late March, so I don’t know my average cycle length. I’m pretty sure it’s around 27-29 days. According to everything I read that means I should ovulate on cycle day 15.

I got pregnant in May (unfortunately ended in MC) and only had sex twice, once on CD 9 and once on CD 23, so I must have ovulated around one of those days because I got pregnant. Do you think CD9 is too early? Or is it possible that the sex on CD 9 got me pregnant but I didn’t ovulate until CD 15 ?

I’ve just had my first period back and now wondering when to try again