What Causes Itching,redness,swelling And Yellow Discharge In Vagina?

i had unprotected sex and then took the Plan B. I got my period but shortly after i have been itching, and its really red and swollen down there? I have a bump on my right lip of my vagina it is sore but not very painful. My discharge is more yellowish and kinda clumpy? I dont see any blisters, do you have any idea what this can be?