Sayang, baby movement tu normal la at 28 weeks, memang diaorang active sangat! But sakit bawah perut yang keluhan you, better check with your doctor or midwife soon, okay? Could be anything from ligament stretching to something else, tak boleh guess-guess. Don't wait if the pain gets worse or ada bleeding/spotting, go to hospital terus. A few of my mum friends experienced similar during pregnancy and it turned out fine after checking, tapi kena confirm dengan doctor. Jangan worry, but do get it checked out ye!