our neeps has something similar sounding to your cat. She gets a very distended and sore belly after she eats... and then has a smelly bum for a while, her belly is tender most of the time and she gets agitated when it hurts, and she almost always smells of poo (we've nicknamed her poo-cat for when she smells).
check how your cat is eating, if it's gulping the food down, give her smaller meals more often or put pingpong balls in to make her move them around to get to her food, should slow her down.
assuming the vet didn't notice a blockage in her intestines, which can cause a backing up of the old plumbing, make sure you feed her high end food rather than cheap tescos food. Sensitive tummy or increased digestable food like royal canin etc do might be best for yours. try making it as bland as possible as your's could also have poor digestion function and rich foods can make the condition worse.
there are pills you can get from pets at home that help digestion and tummy health, probiotics once a week will help also, and cat vitamins might be a good idea too.
we spent 700 on neeps at the vets trying to figure out what was wrong with her but she's still poo-cat lol, she doesn't get a sore belly as much now we have her on petsathome sensitive belly food, she gets half a sachet of wet food a week (meats-sunday as we call it) and she seems to be doing well with this.
you can try and see if your cat is better on an all dry or an all wet diet by doing each for a month and seeing how it goes, take note of smelly days/times and sore belly times etc.
make sure he/she has loads of water to drink, keep cat milk to a minimum as it can make matters worse too, keep it as a treat.
hope yours has nothing bad and just a general tummy disorder.
