Baby still has lots of room to move around at 21 weeks, you don't need to worry or start counting kicks until 28 weeks! But do what ^^^ said and lay on your left side for about an hour and drink something cold and sugary! Follow your gut, if it tells you something is wrong, go into L&D!

As long as your baby is moving you shouldn't be worried. Just drink ice cold water and lay on your side if you get worried