Hi there,
sorry I know this is late, but I am unable to conceive naturally because I don't produce enough oestrogen to ovulate on my own as well. My cycles are regular, but whenever I am been monitored on a natural cycle, I have never ovulated. I have asked my FS what causes this, and the simple answer is, he doesn't know. I appear to be extremely sensitive to anxiety, so if I get stressed, my body reacts by not producing enough Oestrogen. Being monitored appears to be stress enough to cause this as well. Sounds a bit silly, but when I have tracked my cycles, anytime I have been stressed (house buying, job changing etc) my cycle has been longer which translates to late or no ovulation.

Hope this helps - my issue gets lumped in the unexplained infertility bucket as I don't have PCOS or any other underlying issues.