I suspect no leak, a leak to noticably increase consumption would be easily smellable and explosive due to the amount leaked. If you have a good nose the Mercaptin is very noticable. The gas co will send out someone as a courtesy call to walk through and use his Nose and a Gas detector if you say to them you "think" you smell a leak, " Leak " is the word , not High Bill. Usualy in a few hours, as leaks are dangerous and they have a liability.
Check your bill for Therms used , not total price with last year, gas is up, while the gas co is out they will give you an idea of any issues on equipment you have.
Dish soap will detect leaks, but as all others said it is probably something else.
Call the gas co to check out the house, then get out a good Hvac tech, It=A0could be numerous small issues all combined
I just went to the store and bought a 2- Co - Nat Gas detectors for the folks," Nighthawk " a good investment for peace of mind , my Folks do not smell well at 85 yrs old, the microwave was burning [ smelling like a transformer ] and a bad wax ring stunk up the house.... Call the gas co , for a " leak check " it is free..