Std ?

well iim 18 years old and i had protected sex april 28th and about 2 days later i started to have some itching in my vagina ..a couple days later i had "cottage cheese" like discharge and i didn't know what it was so i searched the net and figured it was an yeast infection and searched the net again and found a yogurt remedy and tryed it and it stopped the discharge stopped but the itching didn't stop and i tryed vagisil and it didn't work...well a couple weeks later i found that i started having a yellow to dark yellow discharge and i also inside the lips of my vagina it looked like a rash??? im scaredddd cuz ain't nothing like this happened to me b4 and im really scared! helP!