Eh normal lah at 31 weeks, perut akan terasa tight dan keras especially bila baby bergerak atau Braxton Hicks contractions datang, it's just your uterus practicing! A few of us experienced the same thing and our doctors said it's totally okay as long as takde pain yang severe or bleeding, tapi untuk peace of mind better check with your gynae especially if kencang tu consistent or discomfort sangat, just to rule out anything else.