Normal lang yan, mama! Those are Braxton Hicks contractions, your uterus is just practicing, lalo na when baby is moving around actively at 6 months. A few of us moms experience it more kapag busy kami or dehydrated, so try to rest, drink lots of water, at monitor kung gaano kadami. But if the tightening doesn't ease up after resting, or if may associated pain, bleeding, or discharge, definitely message your OB agad, better safe than sorry lalo na first-time mom ka.