I have no idea about the carb content of Berocca. I'm pretty sure it's sweetened with sugar rather than artificial sweetener, but I don't know how much.
Talk about interesting Berocca mixes, we used to take gin, Berocca and Aspro Clear on hikes/tramps. If you mix it all with water you get a drink which is reminiscent of gin and tonic with lemon, without having to carry the tonic or lemon! Nice and lemony and bubbly......