Birth control not working?

Is there a way to find out if your BC isn’t working, before getting pregnant?

I think I’m ovulating, even though I’ve been on birth control for 3 months. I haven’t missed a day, I was like one hour late the first month for one pill, but I’ve taken them at the exact same time (like a minute or two apart) every day since then.

The only reason I think is because of my CM. I always got this certain CM a little over a week before my period is expected, when I usually ovulate. I’m getting it again this month, i didn’t get it last month or the first month so I’m not sure if it’s just a coincidence or if my BC isn’t actually working lol.

Should I take an opk and see? Or is there any other way to find out?