Sorry teeny, those asterisks go in automatically if a 'rude' word comes up! Some words register as 'rude' words and they are not meant to be! I always get asterisks if I type the word for female dog. Never mind.
Did you mean shih-tzu? I am just guessing. But I don't think it's so important what breed he is. All dogs can have behavioural problems sometimes.
Well, you've had his health checked and he's healthy? So he's not whining to express pain or discomfort? He's not doing it because he desperately wants to go out and can't -is he? Or is a very energetic dog who needs more exercise, and is shut in the house more than he needs?
If no to all that, then it may be that your vet is correct, and he has learned a bad habit.
What do you normally do when he whines?
Do you immediately give him attention? Do you comfort him, try to say everything is okay, and ask him what's the matter?
Even negative attention such as "Oh do shut up!" will be seen by a dog as "attention". Sometimes even saying "No" "Don't do that" or "Don't be naughty".....is no good because it's negative attention.
If he learns that whenever he whines, he gets your response, your love, a treat, or even you connecting with him by telling him to shut up....he will learn to keep doing it.
By positive reinforcement you might be able to discourage him from the habit of whining.
Positive reinforcement might help. Try it. Reward him when he doesn't whine, either with a tiny treat (something very small, especially if you are doing this a number of times a day. You don't want him to get fat!)
And completely ignore him. literally turn your back on him, or get up and walk out of the room, when he whines. Say NOTHING at all to him when he whines.
did not find how to edit this I did not mean to put those asterisks in