Hey man, I know this isn't the info you wanted, but it might help. Quit drinking caffiene altogether, and you will have way more energy than you do with it.

I loved coffee...Coca-cola...Frappuchinos, all that stuff. I had a caffiene addiction. I decided one day to just stop because caffiene is a drug, and it is harmful. I got some violent withdrawal headaches, but found after a couple weeks I was able to 'stay up' and study, and I didn't get that midafternoon slump thing, and I was more awake in the morning than I was with coffee.

Now I have a coke only if I have a headache, and it works faster and better than any otc drug (most of which I am allergic to, so I don't take them anyways).

Best of luck!

Yes, I can only totally agree with Birch's post before.
Quit it totally and you will have much more energy instead.

I am 21 too and I had an addiction about a year ago.
I drank like 5 cups per day and red bull on top of that and
the problem was I could not sleep at night - then needing
more caffeine the next day - again could not sleep, so on.

This is a horrible, horrible vicious cycle that is so hard to
get out of. Quit it and build healthier habits instead.