Hay, first-time mom here too kaya naintindihan ko ang worry mo! Low-lying placenta ay common sa mid-pregnancy, and honestly, marami sa amin na nag-undergo ng repeat ultrasounds lang and it moved on its own by third trimester, so don't panic yet. Best thing is to follow up with your OB on the next visit para ma-monitor mo, at they'll advise kung kailangan mo ng pelvic rest or anything like that depending sa exact position niya, but most cases resolve on their own talaga. Alam ko ang waiting is stressful, pero you're doing great!