Don't worry, mama! At 21 weeks, especially if it's your second baby, it's totally normal na hindi pa malakas ang movements, marami sa amin hindi napapansin ng malinaw until around 22-24 weeks, lalo na kung first trimester pa lang nararamdaman. Since your OB just checked and baby's okay, that's the green light you need! Pero since you're already worried, maybe schedule that checkup soon para ma-ease your mind and mapakinig na sa baby's heartbeat, yan talaga ang best reassurance, at least para sa amin dito.