Extreme vaginal dryness in 21 year old. painful intercourse even when fully aroused and using lube. cause of vaginal dryness?

Vaginal dryness: A lack of vaginal lubricity can be due to a thinning vaginal lining (epithelium) caused by low levels of estrogen hormone. A GYN MD can do a maturation index on a vaginal sample and determine the lack of impact of estrogen on those epithelial cells. Without a multi-folded(rugated)/crypted vagina, moisture will not be forthcoming. This is common in post menopausal women, but not your age. See MD.