I Had My Growth Scan Today At 28 Weeks And

I had my growth scan today at 28 weeks and 5 days but the doctor couldnt find the placenta so he did a vaginal ultrasound to make sure it wasn't covering my cervix which it was not so he then said everything is normal! My question is where is the placenta?? My son is measuring right on point good heart beat and blood flow but im still worried