I started to feel my baby at 18 weeks she usually kicks really low.. Unless they told you that the placenta is laying low in the front you have nothing to worry about.
My placenta is also in the front im 21 weeks
Are you sure they didn't tell you that your placenta is placed more toward the front of your stomach? The placenta can attach at different places with every pregnancy. My baby is located more toward the front of my stomach which makes me feel a lot more movement from him. More than with my first son. That's not anything to worry about if that's what they meant.