Why when I shine a light close to my pupils it doesn't stay the same size? Even after a couple a seconds it keeps changing size.

It is supposed to change size according to the light or dark. In bright light pupils will decrease in size and in the dark they will increase in size.

Not only that, but many people have one pupil that is always a bit wider than the other. I do.

And some of us, they do not change fast enough, causing vision issues when light shone in our face.