What kind of herbs do you take?
Herbs to avoid while using hormonal birth control include St. John’s Wort, Vitex (chasteberry), Red Clover, Black and Blue Cohosh, Fennel, Hops, Dong Quai, Wild Yam, and Licorice.
I'm sure there are more, but this way just with a general search.
You can -- and should-- double check things with your doctor as well.