Not sure precisely when you are in for your Gallbladder op, but good luck - you will be ok and feeling a million times better without the fear of that searing attack!
Presume that you are at home, Cazz, the gaseous feeling will soon past. Just watch for any signs of fever and nail it early with your doc (or duty doc) to prescribe an antibiotic - I let it rumble on for 48+ hours, thinking I could beat it. Hopefully, you won't have any.
The appetite will soon return as well. Hope you are being well looked after.