Bittersweet does not have berries this year
Every year I have had berries on my Bittersweet vines, but this year there isn't any berries. Is there a problem with my vines?
It is possible for part of a Bittersweet vine to die off leaving only a female or male left.
You need both in order to have berries.
I would fertilize in the spring by giving the plant a boost of Phosphorous to promote the berries. Bone Meal is a good way to do this.
Here are some links to help you.