It is possible that you are noticing the cervical mucus that occurs during ovulation. Cervical mucus is thin and stretchy and is produced by the hormone estrogen in the first phase of the menstrual cycle. Ovulation usually occrus 14 days before the beginning of a woman's next menstrual period, and can be charted on a calendar for women with regular menstrual cycles.
How often have you noticed this fluid? Does it occur during fingering every time? Discharge can also be a sign of vaginal infection, so if the fluid smells badly, I'd suggest that it get checked out by a gynecolgist.