Your not using the convector part of the storage heater for heating are you? That would use the full price electric and use it very quickly. The storage heaters tend to work best with them on all the time during the winter months. They are not designed to be an on-demand solution for heat.
If you really wanted to get a sense of your daily or weekly use then I would read the meter and keep a spreadsheet of the readings. That way you would be able to narrow it down to what was using the most units by switching different things on and off during the reading days.