Ayyy normal lang yan, mamsh! At 21 weeks kasi ang baby movements ay subtle pa talaga, minsan parang butterflies or bubbles lang, kaya madaling miss especially if you're busy or if the placenta is in front (anterior placement talaga nakakapagdulot ng ganyan). A few of us din nag-experience ng ganyan, alam mo, some days they're super active, some days parang chill lang sila, it really varies depending on baby's sleep-wake cycle at ang position mo. But honestly, kung nag-worry ka talaga or mas naging mabigat ang concern mo, better to mention it sa OB mo next visit para ma-check properly and mabigyan ka ng peace of mind, kaya lang. Keep monitoring, and as you progress to second and third trimester mas magiging obvious ang movements na yan!