Baby movement..

Terri
Hey can I have a little advice please.. I'm almost 20 weeks with my 2nd child and hardly feel any movement at all :( i have my 20 week scan in a few days so il be asking for some advice.. Also Iv heard if the baby is behind the placenta and the placenta  is at the front of the tummy that might be the reason I'm not feeling baby moving as often.. Thankyou xx