Talk to Gynecologist on Pregnancy Related

Aoa, I’m currently 19 weeks pregnant. I have history of one missed miscarriage at 11 weeks. On my latest visit to dr, she performed an ultrasound herself just to check fetal well being. It was not a detailed ultrasound. She said that baby head is too low. So I should avoid sitting on foot, avoid intercourse etc. I want to ask is this something to worry about? What other precautions should be taken? Secondly, most of the time I’m sitting in bed with pillows on back and straight legs. Is this the correct posture. What postures should be practiced when sitting or lying in bed?