How do I budget my miney?

So my girlfriend, daughter and I are about to buy our first house and I'm scared! I bring home about $2240 a month and when I add up all the bills that I will be paying for I have about 500 left for the month so $125 a week that dosnt go towards bills. That seems fine and dandy to me on paper because I don't feel like I spend 125 a week on useless stuff but my money is always gone! Is there a app or program that can help me budget my money or any advice you guys can give me?