As others have said, you need to look at your bank/credit card statements and work out what you are spending where.
Do you buy a lot of food and drink out of the house - that can cost loads - a coffee on the way to work and a bought lunch can end up costing hundreds of pounds a month.
Have a look at the MSE money makeover for a systematic way to work out your budget and cut costs where possible.
www.moneysavingexpert.com/family/money-help/
Also think about splitting your money up into pots:
All money goes into one account and bills like rent/mortgage, council tax etc comes out of this. Plan to not touch this account for other spending.
Set up a standing order to a savings account for annual and irregular expenditure like Christmas, insurances, holidays, car MOT/insurance/servicing, white goods replacement etc etc. For a typical family this will probably work out at £X hundred pm, so shouldn't be underestimated.
Work out how much you can afford/need to spend on food and petrol/travel and transfer the money to another account. Or you could put these expenses on a credit card and pay it off in full each month by direct debit. Same for child costs - clothes, clubs, bits of money for school etc and also family days out
Finally, you have spending money for adults. Lowest priority if you are short of money. Whatever's left after all the above should be split 50/50 between you and DH. Workout what you spend here on and if you can cut back. As well as lunches/coffees, mobile phone contracts, clothes, accessories, treatments, hobbies etc etc.