I'm 17 and I am experiencing an itchy vagina or probably vaginal lips from sometime :( One day I went down there(used my fingers) and when I brought my fingers back there was something thick on my finger it was off-white in colour and when I pressed it it turned into tiny powder like granules :( What might it be? :(

Could be a yeast infection. Especially if it is itchy.

Some literature: [here].

You should go to your doctor for confirmation.