Could a disease, or infection cause me to miss my period?..?

i think i might have an infection, beacuse i used a mirror and a flash light to look inside my vagina, beacuse ive missed my period for almost 3 weeks..i took a pregnancy test, and it came up negative.. when i looked in the mirror there was white stuff not inside my vagina, but around the clitoris , and lips.. and it smells.. i took a shower, and it still smells.. not as bad.. any ideas what this could possibly be, and if it could be preventing my period?