you may have a leak. Turn off the water at the stop cock in the house and look carefully at the meter for a few minutes to see if it moves up at all.
5 units a week is very high, we use around 100 units a YEAR!, that is less than 2 units a week, for a 3 bedroom house.
I think you have a leak, call the water company, they will be happy to check for leaks , if you are not happy to do it yourself.