I know this will sound painful but when we first got together my husband and I we catergorised everything in a notebook

even if it was a 50c freddo frog, every cent was written down on the day we spent it, then at the end of the week we added up what we spent food, bills etc

then end of month worked out how much we were spending versu how much was comign in, its a real eye opener...we also do it now if we go on extended holidays...so we can keep track of how much we have spent etc

after a few months you will see where those leaks are coming from