It is common. Mine was low but eventually moved up. Praying yours will too.
When my mom was pregnant with me the placenta was below me. The doctor put her on bed rest on her left side to try and move the placenta out of the way so I could come out first and not the placenta. They told her that she could hemorrhage and lose the babyand she could bleed to death. luckily the placenta moved and everything turned out fine for the both of us. Mind you this was in the 80s and they didn't do cesareans. I would say try laying on your left side as much as possible to see if u can get your placenta to move up. Hope my story didn't scare you. At least you have to option of cesarean so you will be fine. Good luck!