Dude, it could be anything.

-her time of the month is coming up.
-birth control.
-stress at work/home/with family/friends
-a vaginal infection


Unless she is faking (which I seriously doubt given what you said), it most likely has asolutely NOTHING to do with you.
Lube is not something that should lower your ego. If a woman gets dry, use it and be happy that science gave us something to rely on when multiple problems cause us to lose wetness.
Try being more confident, maybe even continue foreplay DURING sex a little.
(a.k.a. playing with her clit, dirty talking, etc.)

If that doesnt help, make sure she is happy with your relationship or what may be going on with friends/family. Try to help solve any problems or offer to talk or help.

If THAT doesnt help, maybe she should talk to her gyno about change in diet, washing rituals, hormone balances, medications, etc.


Sorry if I rambled or someone else already said everything Ive said.
Hope it helps.

B