Normal lang yan, mash! At 21+ weeks, ang Braxton Hicks contractions (practice contractions) ay nagsisimula na, kaya parang tumitigas ang tiyan, parang nabuo lang siya ng sarili niya, hindi? Mangyari yan off and on throughout the day, lalo na pag tired ka or dehydrated, so hydrate well at rest when you can. If it's painful, frequent, may spotting, or accompanied ng cramping na di tumigil, better check with your OB just to be safe, pero most likely normal lang yan sa second trimester!