I read on aoa.org that myopia can be caused by visual stress. if so, can relieving stress make your vision go back to normal or get better?

No: The cause of myopia is unknown and likely is due to many causes with genetic predisposition a large factor. This means that if your parents are myopic, you have are likely to be as well. A practical way to think about it is to not worry about it and get the appropriate glasses or contacts to see well. When your myopia becomes stable, typically in the early 20's, it can be cured with the laser.