I used to drink 2 or 3 cups of coffee a day (but only in the morning so it wouldn't mess with my already crappy sleep). I managed to wean myself off coffee earlier this year. Now I just drink a lot of tea. Yum.
Have you ever tried switching to tea around the exam itself? From what I've read it's supposed to have a simultaneous destressing effect (from theanine) which counters the caffeine's stimulating effect.
I drink one cup of caffeinated when I first wake up, then probably two cups of decaf at some point during the day. I'm very sensitive to caffeine so I can't have any except my morning dose. I will drink an occasional cup of hot decaf tea in the evening.