Have you tried keeping a detailed spending diary for a month, just to see where your money actually goes?

Also, do you keep an updateable budget written down somewhere, so you can predict how much cash you'll have available at any point in the monthly cycle? For example, I keep an excel spreadsheet at work for this purpose. That way, even if my bank balance reads +£lots when I've just been paid, then I know I really only have +£sliver of money to spend, because of £X, £Y and £Z etc., standing/one-off/planned charges that'll come out before I'm paid again.

Sorry if all this is in the sucking eggs domain...