My periods are very irregular ranging from 28 to 44 days, usually ovulating around CD 18-33. So I usually start Opk at around day 16. However the only one time I got pregnant was when I had the shortest cycle on my record (about 24 days). hubby and I were not ttc then, but we happened to BD on CD 11, then two days after on CD 13, I had a fever, so my temp got really high. I thought no! It's screwing my bbt record. Around CD 19, I started using OPK, and I got positive ovulation results for 5 days straight. I thought that was really strange and googled about it. Read it online somewhere that said it may mean pregnancy. So on CD 24, I took a pregnancy test and there it was, my first ever BFP. I went to the clinic for a check up, the doc confirmed that I was pregnant. It came as a total surprise to me, still unbelievable to me today. Two weeks later I went to get an ultrasound for the heartbeat of the fetus. Unfortunately the fetus was too small for that , doctor told me to come back a week later to see whether it grew bigger. But a week later, it was gone. I have miscarried naturally. It was like going thru heaven and hell in less than a month...after that miscarriage, I have been ttc again for almost a year and no more BFP so far...