I didn't feel my son kick or move inside of me until about 18 wks, and every day after that day I felt him move, but there were some days when there was not much movement. He turned out to be a very healthy, very active baby who didn't like to sleep much at the beginning
I'm sure everything is fine, it's just that every baby is different......some are more active and some are less active.
My doctor did say that it was very important to feel movement in the last several wks of the pregnancy as the baby grew larger.
Good luck to you!