For those who have used Vitex

I just started taking Vitex this cycle. My cycle was 27 days the first month off BC but had shortened each month and was down to 24 days and I was hoping that Vitex would lengthen my luteal phase a bit (it was down to 9-10 days). I am on CD 25 today with no sign of af yet and tested and got a bfn. I'm thinking the Vitex is just doing its job but I'm wondering how long it took for Vitex to help regulate your cycle? For those of you who have used it how did it affect your cycle length and pms symptoms? I've got very few pms symptoms too.