Ay, I totally feel you, pregnancy pains can be so random, lalo na sa third baby kasi ang body mo na yung nag-adjust na multiple times na! A few of my mum friends said they experienced random sharp pains "down there" when standing up, especially later in pregnancy, and sabi nila it's usually ligament pain or the baby's position shifting, pero honestly kasi bawat pregnancy talaga different, kahit sa same mama. Since it comes and goes at nawawala na after a bit, likely okay lang siya, pero I'd still check with your OB just to be sure lalo na walang pain sa first two pregnancies mo, better safe than sorry na lang, especially pag ganyan ka-advance na sa weeks mo!