Hello snowdragon
Welcome to Purrs.
Can you tell us a little about your cat> Is he elderly, and does he have any other health difficulties? Has this just started since the check up, or was it noticeable before then?
It can be notoriously difficult to get a good look in a cat's mouth to check, and much depends on the cat's willingness to be handled, so it may not be immediately obvious if you take a look yourself as to what's causing the problem.
When Paddy had his teeth out at 15, he had no post surgery difficulty, thank goodness, but if this is something that is happening each time he eats it's best to take him back for a further check up just to make sure everything's settling down with his gums as they should. It does sound like something is making him feel uncomfortable, and your vet should be happy to take another look to make sure all is good.
Cats mouths are not the cleanest of environments, so prudent to make sure there's nothing causing a pocket where food can get trapped and set up an infection.
What is your cat's name? We'd like to say a big "Welcome to the forum" just for him.