I don't think I have heard of anyone allergic to coffee but I suppose you can be allergic to anything - There are plenty of alternatives like teas, hot chocolate. cocoa etc for you to have as a hot drink.
I cannot drink it. I don't know if you could call it an allergy, but it makes me severely nauseous. It can't be the caffeine because neither tea nor caffeinated soft drinks do that to me. In fact, tea calms my nausea.