I had a placenta that wasn't feeding the baby well that was diagnosed by an ultrasound at 20 weeks (baby was very small) I got induced at 33 weeks because my placenta was completely useless and the baby wasn't growing and pretty much starving! My little boy is healthy now, he was 4lbs 10 oz at birth and is now 14 months old and in the 20th percentile for weight and 80th for height. I had to get weekly ultrasounds and nonstress tests twice a week during my pregnancy and see a high risk doctor but everything turned out okay for us. I had a miscarriage before that pregnancy as well so I can understand how stressful it can be. Thinking of you :)
I found out at 20 week scan I had a low lying placenta too, I'm in UK and dont get another scan until 34 weeks to check to see if its moved - if not it will be a planned c section. It is scarey but you cant do anything to change the position of the placenta naturally, and its great you get more scans to keep an eye on baby - Im sure everything will be fine x
I'm sorry i can't help you, but i just wanted to wish you good luck and all the best for what is to follow.