What Is The Itchy Rash On The Arms That Is Spreading?

I drank pretty heavily on Friday night and work up Saturday morning with a rash. The rash only appeared on the upper part of both arms, but was extremely itchy. I drank only a little on Saturday night but did not get drunk, yet at 4:30 am I threw up. Today (Sunday) I still have the rash and it is still pretty itchy and seems to be spreading down my arms. Can you explain what is happening?

I am a female. 21 years old. 5'3" 120lbs.