When to start tracking ovulation

I’m a 28 day cycle gal, but my last one was 38 days. Lol

I bought my fiancé & i some OPK’s from easy@home. I’m just finishing up my period that started on the 23rd (March). When do we start BD & <a href="https://play.google.com/store/apps/details?id=com.glow.android">tracking ovulation</a>?