When I brought my pup for the first time. He was not at all whining when I use to leave him at home alone whenever I go out. Its been almost a year he is with me.
And now suddenly I noticed that whenever I leave him at home, after I lock my door he whines, barks, cry and make noises. Why is this Change in his behavior?

How old is he? If he’s young then it’s probably separation anxiety. If he’s older then it’s possible he wasn’t used to being alone. He had people or other animals to interact with. So he will adjust on his own time.

Dogs go through separation anxiety when the owners leave. The whining is a way to get attention. If you give him attention when he whines you are teaching him how to get your attention. So don’t give him attention for the whining. Also exercising him more helps as well. All the dogs that I’ve had they have all grown out of the separation anxiety. Punishment is not a good tool for attempting to make the whining go away. There are probably lots of tools if you were to Google this.

I see! He is almost 2 years!

Being alone all day is tough on dogs. Consider paying for a doggie day care twice a week, or hire someone to take him for a walk mid-day.

Has he been neutered? That will have effects on his behavior.