Don't know when I'm ovulating?

Kristine • 26. Elementary teacher. Girl born May 18th.
Went off the pill a month ago. Got my fake period a couple days later and then ovulated on scheduled a couple weeks after that. Now I just bled for 12 days. Most was light except for the last few days where it was heavier. Stopped Monday. Should I just start using opk's now until I ovulate since I'm not sure?