I have also take Vitex but would not recommend it as it really messed with my cycle I think it was just too strong
Was the opposite for me. I got a BFP on my first month of taking Vitex - Blackmores brand

Might of just been a co-incidence but I had a 9-day LP hence why I decided to try it.

I guess for you it is a matter of trying it and seeing if it helps you?