What Causes White Vaginal Discharge?

i have white stuff in my vagina.i have had it before.but this time it smells and its ichy.i am not sexualy active. can you tell me what it might be. by the way im 11 and dont want to tel my mom. i have not had my period yet this month . but at the same time my periods always come at a diffrent time.what is wrong with me? :(