New to OPK’s. Help please!

My husband and I are TTC baby 3. Our first two babes just sort of happened without much effort so we didn’t use opk’s. This time we have been trying for 17 months. So our doctor has started having us use opk’s. I got a positive on CD 13 so we BD that night. I got a positive again on CD 14 so we BD again. By CD 15, the second line was still fairly dark, but was lighter than control so not a positive anymore. We BD that day too. Today is CD 16 and my test is very negative today. We did BD one more time today. Is that enough? Should we go one more day? I felt some light cramping last night which makes me think I probably ovulated last night. TIA everyone for the help!