Diet soda

my doc said i could if I let it go flat 1st...so i drink the sprite zero...has no sugar, no carbs and I let it go flat and I have no problems...unless it is not flat..if it has the tinnest bit of carbanation left I double over in pain. So i open it the day before then the day I drink it I shake it up in another container...a lot of work for a flat sprite! Mimi