Rashes after drinking

So i drank a decent amount of vodka mixed with drinks and a couple seltzers and i started to notice a burning feeling on my back. once i got home i realized almost a quarter of my back is red and hurts so bad. i know this wasn’t a sun burn as there was no sun. it’s almost impossible for me to go to slepe right now and i was wondering if anybody knows what this is/when it will go away/how serious it is.