Why have i suddenly lost vaginal elasticity?

Hard to guess: People don't suddenly lose elasticity in their body parts. The elastic fibers that give our tissues elasticity don't suddenly all break at the same time. That means loss of elasticity happens over time, such as part of the aging process, including hormonal changes. However, swelling of tissue, and inflammation or infiltration of tissues such as in auto-immune disorders, can make tissues stiffen.

Vaginal "elasticity": If by "lost elasticity" is meant that intercourse is painful, it could be a lack of lubrication, lack of sexual arousal and/or other psychological changes. There are many commercial lubricants available, and once anticipation of pain is reduced, "natural" lubrication may return.