Even in the womb, baby sleeps most of time especially when you're moving around cos it's like a rocking motion and make them sleep. Normally active during your rest time or bed time but since you're only 21 weeks, it's totally normal to feel like that.
yes of course, baby have they rhytme too. when they play and sleep. you can pay attention when the baby kicks and whats make the baby move. as ussual baby love her moms voice and they kicks to give respons
yes it's normal