Hi Liddy,
You're not alone in your confusion re: Vitex and EPO.
Last cycle I took both Vitex and EPO up until O'ing and stopped. It resulted in a longer LP, 14/14 = 28 day cycle.
I consulted with my Chinese Herbalist who said that taking Vitex through the entire cycle is not an issue, only STOP when pg.

HTH, tho its always recommended consulting with a professional when taking various medications.

All the best
CBG