When I gave up the coffee, I transferred to the diet coke. I was a large an addiction as the coffee. The caffein in the coke is as powerful as coffee. I would drink at least two 16 ounce bottles a day and it would affect me like the coffee. It would speed up my heart rate, keep me up at night and I found that I caught more colds.
I personally do much better on green tea. I enjoy the taste without sugar and have no more than two cups a day. No headaches, fewer colds. I am sooooooooooo glad to not be drinking coffee or cola.
-But to each his own.
Have you checked to see if you're alergic to Aspartame? My ex-wife and several other friends can't eat/drink anything with Aspartame as it gives them monster headaches.
You might take a look at Dite-Rite. It has sucrulose instead of Aspartame, no sodium, no caffine, no calories, no carbs. AFAIK, it's carbonated water, sucrulose and flavor.