Uy, totally normal yan sa 18 weeks, ang ligament pain na yan (round ligament pain) super common talaga pag lumalaki na ang belly, lalo na pag suddenly ka gumagalaw or bumabahing! A few of us moms experienced that din, parang sharp pulling feeling diba, especially pag bigla ka mag-bend or something. Try mo lang mag-slow down a bit pag nag-babahin, and stretching gently before movements really helps, pero kung patuloy na painful or may bleeding, better check with your OB na para sure lang, okay?