Thank you for writing.
Vaginal dryness can happen at any time, even in much younger women than, say, a woman in menopause where this is a common occurrence.
Reasons can include medication or, more often, hormones. Women tend to be far less dry in the middle of their cycle, around the time of ovulation. The driest times are often right after a period. Dryness can also occur close to a period. If you notice this pattern, your natural hormone cycle may be the reason.
If this is sudden for you, or uncomfortable, you can talk with your doctor about why this may be happening.