Baby won’t stop crying

I have the best baby, so when he’s crying I know there’s really something wrong. The only time he ever cries is when he’s hungry, has a dirty diaper, or when he’s tired. He’s 3 weeks old and has slept through the night since he was born. He also usually does not sleep much during the day, hence why he sleeps so good at night. But today he has been sleeping ALL day, which is not normal for him. And the short time that he is awake, he’s screaming his head off. I know he’s not constipated because he pooped yesterday. I seriously have no clue why he could be crying so much. He’s not warm and doesn’t have any symptoms of being sick.