Dodge stalling out?

its really hard to strat my dodge i have to crank it forever to get it to start if it does. I know i have a bad oxygen sensor but im not sure which one i live in chicago so its very cold right now when the car does run it will idle okay but driving is a nightmare if you snap the throttle it will stall and after a little while of diving it just sputters and dies very frequently what could this be?