What would cause your vaginal discharge to decrease?

The context of your question is unclear, but vaginal discharge can vary throughout your cycle, tending to increase prior to ovulation, and if it secondary to a vaginal infection a decrease is a good sign. If you are referring to lubrication during sex, that will vary depending on your level of arousal. Sexual arousal in women is not so obvious as it is in men but, as with men, the level can vary.