RASH! help!?

So my lower back was itching about five hours ago and I thought nothing of it and right now i noticed from my to my chest is covered with pink blotches in radom places......i'm on my second day of antibiotics so i don't know if thats the problem and i'm allergic...but nothing on my face and hands and legs and i feel fine. should i wait till tomorrow or go to the hospital. Its a little after midnight where i am...