I Had Protected Sex Around 4 Am On Sunday And

I had protected sex around 4 am on Sunday and literally after having sex I was experiencing a weird burning feeling on my left labia majora.. Once i took a mirror and looked at my vagina I seen 3 spots on my left labia majora that were pinkish and the next day(Monday-memorial day) my vaginal discharge has a mild odor and is a little yellow .. ive never had an STD before and we had sex once and we were protected . We didnt kiss or have oral or anal sex.. I dont know what to think. I'm not even sure if STD's happen this fast . Im freaking out