fyi - washing your mouth out after performing oral sex on a partner, doesn't decrease your std risk. Std's are transmitted through the sex act itself, they don't lay around and work their way into the body.
A woman's vaginal discharge will change in appearance, odor and taste depending on the time of the month, infections as well as even what she has eaten recently. odds are your partner that you performed oral on didn't have any std causing the off taste but was just something relatively normal.
are you and your current partner aware of your hsv1 statuses since you are engaging in oral sex?
grace
Your risk for an oral STD was very low. I would not be concerned, but to help ease your gf why not have some STD testing done and get a throat swab also.