Vitex delayed ovulation?

Victoria • 33 years old. Mummy of a 5 year old girl and 3 month old boy.

Can vitex delay ovulation? I usually get a positive opk on CD 17 or 18.

I started taking 800 mg of vitex daily at the beginning of this cycle to lengthen my luteal phase.

But I’m on nearing the end of CD 18 and there’s barely even a faint line on the opk.