I'm very confused by this post, and am curious about how you reached the 5GB limit as well, as so little counts against it.

iTunes purchases don't count, Photo Stream doesn't count, etc. I think what you are saying above is that you also have iCloud backing up your iOS devices so therefore it backs up the Camera Roll as well, so yes that could possibly be an issue if you are very tardy about transferring the pictures.

Your email storage also counts, so maybe that's another issue. I have mine set up so that once my email client (Mail on my Mac) moves an email out of the inbox (into a folder for example), then it's also removed from the server. This keeps my inbox from getting too large (I also archive inbox mail every half-year or so). This seems to have the effect of not allowing the inbox to eat up undue space on iCloud.