Momshie, yan ay very common during pregnancy lalo na kapag umaangat ka from lying down or sitting, it's usually ligament stretching, pero since nararamdaman mo sya specifically sa left side, better check with your OB just to make sure everything's okay, especially since you're already 15 weeks along! A few of us mums experienced similar discomfort and our doctors just monitored it, kaya hindi ka nag-iisa dito. Keep me posted ha, sending you comfort vibes!