Fussy baby?

Paola

My baby is 3 weeks old, and he began whimpering and moving a lot in his sleep, a few days ago. He's never done that before. He used to sleep for about 2-3 hours stretch through the night and now he can barely go one hour without waking himself up. I'm concerned about why he is not sleeping as much and what he could be whimpering about. Is he just uncomfortable? Or could he have something else?