Here's what happened to me. Glow suggested I a 6 day fertile window starting on day 5 of my cycle. So hubby and I got going, everyday, perhaps over eagerly! I thought we had done it on best day of ovulation, so we rested. Then had the horrid 2 week wait... Which turned into a 3 week wait with all negative tests. I was so ***** confused! Finally got period. Realised that because it was late, I ovulated late, and turns out we missed my ovulation coz we were 'resting'!! So I advise using ovulation strips, and not trying until a bit later into your fertile window to save up his best swimmers, and carry on trying past your fertile window to cover a late period. That's what I'm practicing this month, so we'll see if it works!!