Honestly, the best thing you can do is also take your bbt each day - you get a special basal body thermometer:
[Here's a link but you can buy it almost anywhere https://www.cvs.com/shop/product-detail/CVS-Digital-Thermometer-Basal?skuId=233142]
You take your temp every morning as soon as you wake up, before antyhing else. You can imput the data into a site like fertilityfriend.com or ovufriend.com and the info you put in can help you find your fertile days in addition to opk's. Once you get a steady temp rise for at least 3 days, you'll know for sure you've ovulated. I was using opk's before I started temping but wasn't sure if I was actually ovulating as you can get several + opk's and not ovulate [your body gears up for it, but fails to actually release an egg]. That's my best advise as sometimes opk's can be very tricky on their own as you're noticing...