How much spending money are we talking about and is this truely after all bills, including those beyond monthly direct debits, eg Christmas, holidays, insurance, repairs to cars, pets, household appliances etc?
What about food and travel, is it separate to this too, or does this come out of your spending money?
Have you looked at your accounts and added up what you spend where?
Different people have different definitions of 'extravagantly' so without any figures it's impossible to say whether you're running out because the amount you have is very small, or you're somehow managing to piss hundreds or thousands of pounds up the wall every month without having anything to show for it.
If you're serious about getting a better handle on your money, have a look at Moneysaving Expert.
Start with the money makeover and do as many things as possible, then get the weekly email and take all the tips in over time. Eg you can get yourself a free £100-150 at the moment by switching your bank account. Some people do this over time and have 'burner' accounts to facilitate this, making hundreds of pounds in free money.
Depending on what you get up to, areas to look at are food and drink out of the house, if you do this a lot, it costs a lot, and is far more expensive than eating at home.
Also cutting down your TV, broadband etc. Absolutely no reason at all to pay full price, there's always a discount available.
www.moneysavingexpert.com/family/money-help/