Try not to worry, 21 days is just a guide.
When you set your eggs did you count the day you set as day 1 or did you count day 1 after a full 24 hours of incubation? Have your temps been ok during incubation?
By Day 22 you should be getting signs of life (chirping, tapping shell, etc.). I wouldn't give up hope yet-- they might just be taking a bit longer to get going. You should candle them to see if there is movement inside the eggs.