Oo normal yan sa second trimester, mama! Ang ligaments mo (round ligaments) ay nag-estretch pa lang habang lumalaki ang baby at uterus mo, kaya yan yung matigas na feeling at slight pain kapag nagbago ka ng position or nag-stand up agad, a few of us felt exactly that around 17-18 weeks. Yung pag-kapa mo ng matigas part ay baka yun na yung uterus mo mismo or even the baby's movements/position na nag-settle, so totally fine, pero if the pain becomes sharp, persistent, or may heavy bleeding, better to check with your OB just to be sure!