Sprained ankle 3 weeks ago, and it gets swollen during day, but when I wake up it is regular size. Why?

Sprains take a long time to heal. When you are up and around you are irritating the sprain as well as the location of your ankle in relationship to your heart. This is where the swelling comes from. when you go to bed your injury is elevated and you are not irritating it. This is a normal response for a sprained ankle. Periodic rest periods during the day with your ankle elevated and iced will help to alleviate the symptoms while your body continues to heal.