Eh, normal lah tu at 24 weeks! A few of us experienced the same thing, perut mengeras kejap-kejap adalah Braxton Hicks contractions, basically your uterus practice contractions. Tapi kalau ia frequent, painful, atau ada spotting, better check with your doctor just to be safe ya, sometimes they want to rule out things like early labour or uterine irritation. Try to rest, drink more water, and avoid stress, memang membantu jugak kat aku dulu.