For About A Week Now Ive Been Having A Rash

For about a week now ive been having a rash down by my anus. Its been burning a lot and it hurts to poop. Just the other day i noticed it starting to spread to my vagina and now it burns when i pee. It burns alot and sometime i want to hold in my poop because it burns but i can't hold it in. I dont know what it is. But please help me to try to cure it asap