Last week, my 2014 Sentra's the engine light went on and OBDII scanner reads a P0303 code which is cylinder 3 misfire issue. Nothing seems wrong, engine seems working smoothly, no vibration or acceleration issue.
So I cleared the code using the scanner. The next day, I can see the remaining mileage drops quite fast like 5km(3miles) every couple of minutes, both on urban road and highway. It only decreases when I put foot on the gas, it will increase back some when waiting at traffic light.

As the spark plugs has been replaced last year, so just got the coil pack replaced yesterday. But the issue seems still there. with a pretty much a full tank of regular gas, drove just under 100km(60mile), a quarter of the gas tank is empty, which is like 10-12L(3gal) more or less.

I googled online, for possible causes, but seems normally people will try to check spark plugs->coil pack->spark plug wire(this one doesn't have)->fuel injector, vacuum etc.

So I don't feel any difference when drive the car except the gas consumption is like 50% higher than before. I am wondering if anyone have any clue what else could go wrong or need to check next?

Thanks in advance.