vitex (agnus castus).....

Looking for a little advice or anyone in similar situation to me! I've got PCOS and had very irregular af for a year now since coming off the pill. I have been taking agnus castus (aka vitex) tablets for two weeks now as I've heard good things. Just had a few days of brown spotting/very light period? Any ideas what this may be as it wasn't like a normal period? Any success stories would be great! I've also no idea when I ovulate as they come back as high fertility most of the time :/ xx